Praise the sun. Our Dark Souls Walkthrough provides tips for surviving the adventure, a guide to the entire world, and hints for slaying bosses.
You can only enter Anor Londo once you clear Sen's Fortress. When you best the Iron Golem boss, a circular ring of light will appear. You can investigate it to catch a ride from some gargoyles. They'll take you directly to the entrance of Anor Londo. You can talk to the gargoyle nearby if you need to leave, as well.
Anor Londo is full of powerful enemies, so prepare for a bit of a struggle as you acclimate yourself. Start down the stairs and you'll be able to descend a fair amount of time before you meet your first enemy, a towering guard with a huge shield and spear. He's not as bad as he looks, if you can draw him out and pelt him with Fireball magic or some firebombs, but he can inflict some serious pain on you if you don't block his attacks (or even if you do block but then lose too much stamina). Though he is a fearsome foe and you have tight quarters in which to defeat him, you've won battles like this in the past and should do fine here.
Past that knight, the stairs continue to descend and then you can head left into another room. Here, look left and you'll see a pair of the knights like the one that you just defeated. With projectiles or magic, you can draw the closest fellow to you first. Defeat him, then lure his fellow toward you and repeat the process. Just make sure that you're not stuck fighting them both at once.
After those encounters, you're likely running low on resources. However, you can proceed right and through the doorway to arrive in a large courtyard area. Resume your trek forward and ahead you'll see a building with some enemies standing guard. To your left and right, there are two other buildings. Start by heading left and down some stairs, where you'll find an area bonfire. There's also an NPC in the area. Talk to her and she'll say that you can head upstairs and proceed directly ahead to perhaps meet with Gwyn.
Head up the stairs as directed, but you still have some exploring to do. Head left and you will find another chamber like the one you just cleared a moment ago, with a couple of the fearsome knights. Defeat them, then check the chests that they were guarding. The left one contains Twinkling Titanite and the right one is a Mimic enemy. Defeat it to obtain the Crystal Halberd. If you want, you can head outside and past the knight to find a grassy trail that leads up to an opening, but the opening is presently sealed and can't be passed until later.
For now, return and rest at the bonfire before you climb the steps again and this time proceed directly across the courtyard. You'll find an elevator, which you should ride down to the lower level. Descend some steps and start out of the building to see a winged gargoyle. As you start down the wide steps that lead to the pathway it occupies, the beast will rush you. Let it come to you, then greet it with the attack you favor. Fireball magic works great, or firebombs. The beast is able to move pretty quickly, despite its girth, but you can use ranged attacks as you back up the stairs and you'll be at only minimal risk.
When the gargoyle is toast, head down the steps and then look to the left from the base of the steps. There's an opening to the side where you can drop carefully down to a lower level. Head along that level and pass through an archway to the left side. In that direction, you can find Demon Titanite in a chest. Snag it, then head back through the archway and look ahead to the nearby building. You'll notice some steep platforms rising toward it. You can climb along this nearest platform, dubious though it may seem, and arrive above a balcony that extends from that upper building. Drop down to the balcony and step through a hole in the glass windows.
As you start inside, you'll be attacked by two assassins with throwing knives who drop down from an upper balcony along the room's closest edge. They're weak foes if you get in close and slash them apart.
Past those enemies, you'll find a ladder that you can easily ascend. Do so and then look out over the area ahead of you. There are narrow ceiling beams spanning the area. You can climb out along those beams and work slowly across, though along the way you'll be greeted by the assassins. You might try picking them off from a distance with projectiles to get them to rush you, since their ability to move quickly without jumping to their doom is as limited as yours.
Continue carefully along the ceiling beams and you'll reach a chandelier at the center. You can try dropping onto the chandelier, which has a corpse and item on it, but your weight will break the chandelier and it will plummet to the floor. The fall is too much and you'll die in the process, but at least the item will be left on the floor of the building where you can snag it later. You could always try hacking the chain with a weapon instead to see if that achieves the same net end.
Continue along the room. As you near the far side, it's important that you be careful because there are two more knife-throwing assassins who may try to rush you. If possible, you want to take them out with projectiles or magic before they get near you. While it's true that sometimes they will just fall without your intervention, those few instances where they don't can really suck because it's difficult to fight when a few steps to either side will find you falling to your death.
When you reach the far side of the chamber, you can descend a ladder to find a mist-shrouded door on the right side of the chamber. You're still high above the lowest floor of the cathedral building, but the door is progress. Note that you can go past it to find stairs that lead to an area with some pillars and there's an assassin to kill, but otherwise that detour is unremarkable. Pass through the mist-covered door.
On the other side of that doorway, you'll find a lever to the left. That seems promising, but at least for now it won't move. Start forward along the nearby walkway and you'll come to a center area with a huge lever at the center. It looks like a gear with a stick protruding from its side. You can interact with the protrusion to turn the gear. Doing so will cause the platform to twist and turn as it descends toward an area below. You're now in the vicinity of the area where you fought the first gargoyle, which is interesting because now you'll be attacked by a second one. Defeat it in the same manner that you did the first (though now there are stone columns that can get in the way or give you shelter from its attacks, depending on how you fight). Then look ahead of you. There are high stone steps leading to an area densely populated by enemies.
Before you proceed, go ahead and backtrack to the bonfire (which is now only a short distance away, with the platform properly moved). Then return to the platform.
Before you continue forward and up the steps, you may wish to make a dangerous but potentially lucrative detour. Because the location of the platform has moved, it's now possible to descend its steps and reach the lower entrance of the cathedral area you explored before. This should be done with caution, however. The cathedral's lower level is populated by a bunch of assassins and they can be difficult to pick off if they're swarming you. If you decide to enter the cathedral, take a methodical approach that allows you to lure one toward you at a time so that you're not swarmed.
The item that fell with the chandelier when you were moving through the rafters, you'll find, was the Great Magic Weapon sorcery. If you head along the room to the back corner (near the conspicuously large and hideous painting along the back wall), you'll find a corpse that you can loot to receive the Black Iron Helm, the Black Iron Armor, the Black Iron Gauntlets, the Black Iron Leggings and the Black Iron Greatshield. Then you're done here, at least for now.
Return to the pedestal with the lever and give it another twist in the same direction to drop it down one more level. Then descend along the stairs and you'll find a small chapel area. As you approach, make sure that you have the Darkmoon Seance Ring equipped (you will have found it in the Catacombs area if you've been following this walkthrough). As you head into the building, you'll find a bonfire ahead of you. Put it to use and step forward to investigate a nearby corpse. As you approach, a wall will vanish in front of you because you're wearing the ring. Check the corpse for the Ring of the Sun's Firstborn, then head down the stairs where the wall had been. At the base of those stairs, you'll be spoken to by a voice and then you can step forward and press the on-screen prompt to kneel. Agree to enter the covenant and you'll receive the Blue Eye Orb and the Darkmoon Blade Covenant Ring.
Now backtrack the way you came. Turn the lever again and ride the elevator up. When you're ready, start forward toward the enemy-infested steps that you noticed previously.
As you begin advancing up the steps, you're in for an unpleasant surprise. Two of the huge knights with shields will rush you at the same time. Back away and rely on fire attacks to weaken or kill them, preferably one of them almost immediately so you only have to focus on dodging the attacks of one knight. You should be capable of dancing around these fellows by this stage in the game.
When they go down, keep climbing to the top of the area and you'll find mostly locked doors. The exception is the area to the right, where you can come out on the top of some stairs that descend to a cluster of sickly looking white gargoyles. They are able to attack with pretty good range and their spears are of the lightning element. If you have any fire magic left, you can use that. You can also push the gargoyles back toward the edge of the ledge to trick them into falling off, which kills them (even though you'd think they could fly). Try to lure one toward you at a time so that you don't have to deal with too much at once.
After killing the gargoyles, descend along the steep slope ahead of you (which looks a lot like the one you climbed to enter the cathedral's upper level). Near the base, pause to prepare. As you start forward through the pillars, two gargoyles will try to rush you. If you target one, you can easily back up along the ledge you just descended and force them to follow you so that you can worry about one at a time. You may even be able to use a spell like Great Chaos Fireball to hit them and take out both gargoyles when they're clustered close together.
Now you need to keep up the streak and look to the area left of where the gargoyles tried to trap you in the pincer attack from behind the pillars. Up on a ledge above, there are two snipers positioned. They'll fire arrows as you try to approach, and the only way to climb is up the steep ledge. Move quickly with your shield raised and ascend to the first ledge, which provides a wall you can use for shelter.
You've now reached the tricky part. You need to head around the ledge and climb a second of the ledges like the one you just climbed, and you need to do so quickly enough that no arrows hit you and knock you from your perch. It's actually quite difficult to do. Try the right side. Wait at the wall for an arrow to hit it, then head quickly forward at your normal walk speed. In a steady manner, head forward and then around the corner to the left and then start up the steep ledge. Now as you near the top, you need to head right and rush the knight. Roll under any arrow he fires while hugging the wall, then get close and hit him with your attacks before he can fire another shot. Hit him before he can shoot you, then hopefully you'll knock him off the ledge and to his death.
Once the knight is toast, you can follow the ledge around to the back side and drop down to the balcony where a mist-shrouded door waits. Pass through it to find yourself in a long hallway. Take the first door on your left, which opens without a key, and you'll find a room with a bonfire and Solaire.
Now that you've saved, explore the rest of your immediate surroundings. The doorway on the opposite side of the hallway leads to a room with a silver knight. You can hit him from a distance with fire magic if you want to cheese the fight, or you can apply more standard practices to play fair. However, know that the knight is capable of leeching through your stamina and even if you survive a flurry of blows with his long weapon, you'll be too weak to retaliate. That can get old fast, so it's better if you can dodge and step around from behind to deal a quick blow to the back. After killing the knight, he may drop the Silver Knight Spear. Open the treasure chest he was guarding to find a Sunlight Medal.
Return to the main hallway and you'll find some stairs to climb. Ignore them and head around the back side to find another silver knight. Defeat him, then try the doors. One is locked from the other side, but you can enter the other one to find an empty room. Check the fireplace and roll through the brickwork along its back side. You'll find a hidden room with a descending staircase. Head down the stairs and at their base, you will find a huge, dim room with a lot of pillars. Near the back corner, you can check a series of treasure chests. They contain, from left (starting with the lone chest) to right: a Mimic monster that drops the Occult Club, a Dragon Tooth, Havel's Greatshield, Havel's Helm and Havel's Armor (in a single chest) and finally Havel's Gauntlets and Havel's Leggings in the last chest.
Return upstairs and now you're ready to ascend the large spiral staircase. It will take you to a landing where you should walk out carefully (rather than continuing to climb) and watch your back. There's another silver knight here and he'll surprise attack. Defeat him, then check one corner of the room to find a Mimic that hopes you'll think it's a treasure chest. Defeat it for the Gold Coin that it is carrying.
While you're on this floor, look around some more. You'll find another of the knights at the end of a hallway. He's the other of the two snipers who made life so difficult as you were ascending to this tower. Have your revenge on him now. Then you can explore the side rooms. As you head back from taking out the knight, the door on the left is locked but the door to the right leads to a dress room. There's another door there, near the painting, which you can open to find another of the silver knights just right of the doorway. Take him out as usual, then check the edge of the room for a spiral staircase. Climb it and you'll find yourself on an open rooftop.
Ahead of you on the rooftop, there's a silver knight standing in a door. Another one (this one armed with a bow) is in a doorway to the right. Start with the nearer knight and eliminate him quickly, then take out the other knight just to be safe. Now you can check the rooms that they were guarding, which lead to stairs in both cases. The room that was just ahead of you will let you descend to find Sir Onion (the character you last met outside of Sen's Fortress) in front of a door. Open the door, but be careful about passing through; there's a knight waiting to the right. Kill him, then look along the room. There are two more knights waiting to challenge you. Kill them by luring them toward you one at a time and fighting on the opposite side of the corridor. Then open the treasure chest that they were guarding, which is near the side of a bed. You'll find two Demon Titanite.
Open the door just to the left and now you are back in the familiar hallway. Head forward and there's another Mimic pretending to be a chest. Defeat it for five of the Silver Coin item. Then open another nearby doorway, near the Mimic you just defeated, and ahead of you there is a knight. He won't move to attack unless you get near or start to the right, where you can find the Soul of a Hero on a corpse.
In this same room, look over the railing and you'll see a room below you. There, a monster is wandering around. It's one of the powerful beasts like the one near the blacksmith in the Undead Parish. You've now explored most of this upper tower, but you still haven't come face-to-face with that beast. It's time to change that, so go ahead and return to the tower roof.
Previously when you came to the roof (assuming you've been following our instructions), you had two options about where to head. You had initially gone straight, and descended stairs after defeating a knight there. This time, you'll want to head across the rooftop to the lone staircase on the side of the building opposite where the two smaller towers are close together. Defeat the knight that stands guard with his sword and bow, then descend the stairs. You'll arrive finally at a new intersection. There are doors to the left and right, or you can proceed directly up a high staircase.
Start with the door to the right. There are two knights in this room, one partway down the staircase and another hiding near a door at the bottom of the room. Defeat them carefully as you battle along the stairs, then open the chests he was guarding. You'll find the Silver Knight Helm and Silver Knight Armor in one of them and the Silver Knight Gauntlets and Silver Knight Leggings in the other. Then you should open the nearby door, which creates a shortcut into the hallway from which the room with the bonfire branches.
Head back upstairs to the intersection and this time, go in the door that was to the left side of the path instead of to the right. You'll find the huge monster that you previous observed from an upper balcony. It can be tough to battle him in such confined space, especially because he now has a much, much larger life meter and is capable of inflicting more severe damage. If you fight him and win (make sure you get behind him to increase your chances or he'll just pound you repeatedly and kill you almost before the battle even begins), though, you'll always have the memories.
Now you should head back to the intersection and ascend the long staircase that you saw ahead of you. It leads to a higher landing where you can start to the left and find two choices about how to proceed. You can either ascend a set of steps along the wall, or you can descend into a wider room below.
Note that there are two giants in this room, powerful enemies that can severely ruin your chance at glory if you rush down and try to fight them fairly. However, from the vantage point above, you can perhaps snipe them with shots from your arrow (if you brought plenty of arrows) and take them out without engaging them directly. If you land a few poison status effects, things will go almost smoothly. Then you can descend to the lower floor and head toward the locked double doors (though you should watch out for an archer on the stairs on the opposite side of the room). To their left as you approach, there's a lever that you can pull. Doing so will create a shortcut leading back to the early portions of the stage. Then you can cross to the far side of the chamber, climb some steps and enter the mist-shrouded door to fight the area boss. Alternatively, you can finish exploring the area first.
If you head up the stairs at the intersection rather than descending to take care of the giants and activate the shortcut, you'll find a high series of glass windows. One is busted. You can drop out of it onto a ledge, then descend along a building to find yourself back outside, overlooking the early portions of the stage. You can head around the wall and drop down to collect items that are guarded by gargoyles. You'll find the Dragonslayer Greatbow and Dragonslayer Arrow on a single corpse. There's also a Titanite Chunk nearby, if you drop down through a hole in the fence and head left to battle some more gargoyles. Finally, you can also find a blacksmith in this area if you head in the nearby door. Then you can ascend some stairs to arrive back in the main chamber ahead of the boss, but on the other side.
When everything is settled, go ahead and make your way to the boss chamber. It's time to prove definitively that you're better than anything Anor Londo has to throw at you.
Dragon Slayer Ornstein and Executioner Smough
This battle is actually against two bosses at once: Dragon Slayer Ornstein and Executioner Smough. You'll need to focus on taking one of them out at a time so that you don't have to spend the whole fight dodging attacks from the both of them. Which one you take care of first is entirely up to you and should be determined by who you most would like to vanquish ahead of the fight's more difficult second half.
Dragon Slayer Ornstein is the faster of the two, but in general less lethal. He attacks with a Lightning Spear, so you would do well to bring gear with strong defense against that. Smough hops around, settles, charges and then resumes leaping around the area. You should hit him after he lands and strikes. He's weak against good pyromancy magic, but you'll have to spend a lot of hits to take him out for good. He drops the Leo Ring when defeated.
Executioner Smough brings a heavy hammer that he can use to break apart the architecture as you battle. His moves are much easier to avoid and you can even block the horizontal swings if you have a good shield. Be careful, though, because the weapon has longer range than you might suppose. hat's especially true since Smough is capable of leaping a short distance and hammering down to send small shockwaves a short distance from wherever the hammer strikes. Not only that, but he'll happily use his girth against you. Make sure to avoid his charges.
When you defeat one of the two, the other will get all grumpy about it and will attack more ferociously (and with powers gained from his fallen comrade). Regardless of how much damage you have done to both characters throughout the fight up to that point, the remaining warrior will also have full HP. To win, just keep following your same general strategies that have taken you to the fight's halfway point and dodge out of the way for some estus healing when necessary. There probably won't be a lot of that happening, though, because your foe is suddenly capable of one-hit kills (especially if the one remaining is Smough; he practically turns into a lightning freight train and about the only way to avoid him is to circle around the remnants of the pillars that he probably smashed earlier in the fight). If you fall in battle before taking out Smough and Ornstein, both bosses will be alive again the next time you encounter them, even if you slew one of them.
Once you win the battle against Ornstein and Smough, you'll receive the Soul of Smough. Your reward for victory over the pair is 30,000 souls.
Head to the back left side of the room and there's a lift that you can ride to an upper balcony, where there's a bonfire that you can light. Nearby, some stairs lead up to a side room. Open the doors and head inside, where you'll meet Gwynevere. Kneel before her and she will hand over the Lordvessel, which allows you to warp between bonfires. After that, you can kneel again and you will have the opportunity to join the Princess's Guard covenant. If you agree to do so, you'll receive the Ring of the Sun Princess.
Now you're done in the area. You can go ahead and exit now. The most convenient way to do so is to head to the bonfire and use the new 'Warp' option. You can teleport instantly to bonfires at a number of locations you may have visited on your journey so far. It's a real time saver.