Endless stairs

"To open the door that leads to the "endless" stairs, you need 70 Stars. Bwa ha ha!"

- Bowser

The Endless Stairs (stylized in game as the "endless" stairs) is an obstacle within Princess Peach's Castle first appearing in Super Mario 64, and later reappearing in Super Mario 64 DS. It is behind the final Star Door, which leads to Bowser in the Sky. If the player has less than 70 Power Stars in Super Mario 64 and 80 Power Stars or don't have Mario in Super Mario 64 DS, they can still enter the Star Door, but they will endlessly climb this flight of stairs. If the player turns back after climbing the stairs for some time, it's like they never went anywhere. Once the player manages to collect 70 Power Stars (80 and Mario in the Nintendo DS remake), the Endless Stairs finally ends.

Media
The audio track that plays seems to be based off of the Shepard tone audio illusion.

Trivia

 * There is a glitch with which the player can bypass ever needing to collect at least 70 Power Stars, but only for the Nintendo 64 version.
 * The "endless" stairs illusion was created by warping Mario back once he reaches a certain point.