The Basement is a secret feature of Geometry Dash since Update 2.1 and Geometry Dash World. It is located through the Vault of Secrets from a door in the lower right corner, requiring the secret level The Challenge to be completed.
The Basement contains a locked cell, a torch on the left and a skull and chain in the foreground. Initially, there is a chest in the lower right corner which contains a cube. A pair of glowing green eyes will soon appear and an unnamed creature inside will exchange dialogue before a series of locks appear to the right. Selecting each lock will provide instructions on how to acquire its respective key and trigger the associated location.
- The green key is found in the first large chest from the Treasure Room, which requires 50 chests to be opened.
- The blue key is rewarded for completing the Chaos Gauntlet.
- The orange key is found in the chest in the Chamber of Time.
Selecting each lock after possessing its respective key will remove it, until all three locks have been removed. This causes the bars to descend from the cell, freeing the green creature as it is revealed to have shoulders, large horns and a toothy smile. It and the Keymaster exchange dialogue before a large chest appears in the cage containing a cube, a death effect and a purple key which unlocks the Demon Gauntlet.