Toy Block Door

From the Super Mario Wiki

The Toy Block Door is an item in the game Wario Land 4. The Toy Block Door is a Door like any other door except it's locked and needs a Triangle Toy Block to be opened. The door looks like a thing made of small red and yellow blocks with a Triangle Toy Block slot above the closed multi colored door. These doors only appear in The Toy Block Tower stage which is found in the Topaz Passage.