The Princess's Secret Slide

The Princess's Secret Slide is one of three secret levels in Super Mario 64 and Super Mario 64 DS, where Mario must simply ride a winding slide to the bottom, where a Power Star awaits him in a ! Block.

There is also a second Power Star that will appear if Mario can get to the bottom of the slide in under twenty-one seconds.

The entrance to the slide is on the first floor, atop the central staircase, and behind the star door labeled "1", meaning it would require 1 Power Star to enter. In the room behind the door are three identical stained glass windows with images of Princess Peach on them. The one on the right is the entrance to the slide.

Here's a Gltch discovered by SMB Madman:

When you enter the slide with at least half of your health, slide down and jump off to the edge of the lower part of the slide WITHOUT ground pounding. Mario will lose all his health and fall out the slide. When he enters the castle, Mario will lose a life.