Legend of Zelda: Oracle of Seasons

Another quick dash into Subrosia (don't they make creamed rice?) to grab the Magical Doofrey of Autumnanulness for my wand, and then it was off to heave mushrooms out of the ground and enter Dungeon 5.

There's a lot of water in there. And minecarts. I've found the map and compass, and a small key, but now I'm not too sure where to go next. Luckily, this dungeon looks pretty small, so I'm hoping it won't take too long.