The Legend of Zelda: The Wind Waker -
Play the Song of Passing to return to daytime. Walk passed the archway and you'll see a man sitting on the steps next to the auction house. Speak to him a few times and say that you completely understand him. He tasks you with getting a picture of a pale, perfectly round thing. Luckily, we just did that. Show him the picture of the full moon that you just captured. As a reward, he will give Link Treasure Chart #31.