Pipe Land Coin Treasury
From the Super Mario Wiki
In The Adventures of Super Mario Bros. 3 episode Misadventure of Mighty Plumber, Bowser and Mighty Plumber breaks into it through the Maze, when Mighty Plumber is convinced that Mario and Luigi are trying to steal it, and they have to get all the Coins inside to Castle Koopa.
Once King Koopa gets the money, he locks Mighty Plumber inside and escapes, when a security system consisting of a flood came out. Mario and Luigi appear and free him, and they are able to stop King Koopa from escaping with the Coins.