File:Sunkin ship.PNG
It's a sunkin ghost ship.
A wrecked ship in Super Mario World that serves as a gate to the Valley of Bowser. After defeating Wendy O. Koopa, Mario has to swim through this ship in order to make the doorway to World 7 come out of the sea. On board the ship are some Bill Blasters, Floating Mines, Koopas, and a massive swarm of Disappearing Boo Buddies.
It's one of the Koopaling's Airships from Super Mario Bros. 3. Probably Larry Koopa's because his castle is in the Valley of Bowser.