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 two Power Stars can be found. It's also one of the four courses in the multiplayer version of Super Mario 64 DS. The first star is at the star, the second at the middle, and the last three at the end. The end is the best place for fighting.

The entrance to the slide is on the first floor, atop the central staircase, and behind the star door labeled "1", meaning it will require 1 Power Star to enter. In the room behind the door are three (two in Super Mario 64 DS) 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 will not lose a life, but will be sent back to the castle lobby. Like other secret levels, the player can lose a life by taking damage until it reaches zero. In this case, the only way to take damage is to jump from the first part of the slide to the second part of the slide, resulting in damage due to falling from heights. This is the only secret course that contains Blue Coins. There is also a hidden platform with grey bricks.

The room that housed the entrance to the slide was redesigned in the DS version to also serve as character select and Rec Room entrance. But an early version of the room, based on the N64 version, can be found in the game's files. There's a sign that says "Bowser dosen't know about the hidden star here" which the under 21 seconds one.

! Block
Mario must ride the slide all the way to the bottom and hit the ! Block to collect the Power Star.

21 Sec.
This second Star will only appear if the player reaches the bottom of the slide in under 21 seconds. This Star will appear in front of the ! block that contained the first star.

Trivia

 * The tune that plays in the course is a variation of the Bob-omb Battlefield theme (aka, the main theme of the game), as well as Cool, Cool Mountain's music. The music is also remixed in Super Smash Bros. Melee, as well as in Super Mario Galaxy 2 in the Tall Trunk Galaxy level "Tall Trunk's Big Slide", and in the Rolling Coaster Galaxy. Another remix can be heard in Paper Mario: Sticker Star in Bowser's Snow Fort, during the mine cart sections. Super Mario 3D World features another variation that plays while riding Plessie. The latest remix is heard in Captain Toad: Treasure Tracker where it plays during part of the Coins Galore minigames.
 * This course is the only course in Super Mario 64 that has no Red Coins mission.
 * There is a glitchy shortcut which allows players save about 7 seconds.
 * Most secret courses have this music. The main courses that have it are the mysterious slide in Tall, Tall Mountain, Tick Tock Clock, and Rainbow Ride.
 * All courses in VS. Mode have this music, including Sunshine Isles, which had music from Super Mario Sunshine.