Climb back up to the windmill carts. Equip a fire arrow and fire it into the lighthouse bellow as you pass it, which will ignite the lighthouse and reveal an invisible chest on an island. Talk to the man standing near the upper-level windmill door, and he'll give you a piece of heart. Then head over to the outcropping near the bomb shop and use the deku leaf to glide to the previously invisible chest, which contains another piece of heart.
Enter the auction house, which is next to the Chuchu Jelly Shop. There are three prizes you'll want here: two treasure charts and a piece of heart. You'll have to win four auctions to get them all (the first will give you a joy pendant). If you don't mind spending a lot of money, wait until the auction is more than half over, and then start bidding like crazy. You'll stun the other participants if you bid significantly more than the previous bid, and you can raise your own bids while they are stunned. If you want to play it safe, get your bid meter down and wait until the auction has less than 10 seconds left. Bid high to stun the competition for the remainder of the auction.
If you're trying to complete the Nintendo Gallery (see that section for details), visit Lenzo at night. He'll give you a legendary pictograph. There are seven in all, and he'll give them out according to the phase of the moon.
There are a few more tasks to complete here, but they will have to wait until you've rescued Aryll from the Forsaken Fortress. It's time to head there now.