suppermariobroth:

In Super Mario Bros. 3, the rock between the path to the first fortress in World 4 and the Spade Panel can be destroyed with a Hammer item, allowing the player to bypass the fortress. There is no obvious indication that this rock is destructible, as it is surrounded by decorative rocks. In fact, many guides for Super Mario Bros. 3 do not mention this shortcut. (Footage recorded by me in a NES emulator.)