Behind the Waterfall

Cavern of the Metal Cap is a cave in Super Mario 64 that contains the Metal Cap's ! Switch. The entrance is located in Hazy Maze Cave, behind the double doors in the underground lake.

The cave is decorated with large glittering crystals and has a stream running through the middle. The water is moving very fast and can sweep Mario out the cave's one-way exit, the waterfall outside Peach's Castle. Upon entering the cave, Mario is automatically turned into Metal Mario and invulnerable to the stream's current. If the player hurries, they can quickly defeat the few Snufits guarding the Green ! Switch and press it. All the green ! Blocks in the game will activate, granting access to the Metal Cap.

In Super Mario 64 DS, the area was retitled Behind the Waterfall, and the Green ! Switch was removed. However, a second Power Star was added, which can only be reached by Mario via a Power Flower.

Missions
There are only two missions seen in this level.

Star 1
Eight Red Coins are in the area, and several of them are just below a huge waterfall supplying the stream. The only way to reach them is by becoming Metal Mario/Wario.

Star 2 (DS only)
Using Mario, the player must hit the ! Block by the waterfall to obtain a Power Flower. By floating upwards from that spot, they can find a Power Star up above.