Trapdoor (Wario World)
From the Super Mario Wiki
Trapdoors are doors that lead to Bonus Areas, found in the game Wario World. There are two types of trapdoor: wooden and steel. Wooden Trapdoors feature small obstacle courses, which are usually underground. They are distinguishable from steel Trapdoors by the "X" shape of bandages on them. Wario can enter them by Ground Pounding them. Trapdoors reward the player with a red diamond, and possibly a Gold Statue piece.
Unlike wooden Trapdoors, which can be entered with a Ground Pound, steel Trapdoors require a Piledriver to get through. Once inside, Wario finds himself in an expansive obstacle course in the sky, with no solid ground at all. Falling off the floating platforms forces him to start over. At the end of the obstacle course, a Red Diamond is always found. Sometimes, a Golden Statue Piece is there as well.