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 two Power Stars can be found at the bottom.
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. In the DS version, the room is expanded to hold the character doors but the slide itself remains the same and is still accessed via a picture of Peach in the same room. If Mario falls off, he won't lose a life, but will be sent back to the castle lobby.
This second Star will only appear if the player reaches the bottom of the slide in under twenty-one seconds. This Star will appear behind the first Star.