The Basement is a secret feature of Geometry Dash and Geometry Dash World (limited), being introduced in Update 2.1. 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. After selecting the back button during the first visit, a pair of glowing green eyes will appear and an unnamed creature inside, elsewhere referred to by the Keymaster as the Demon Guardian, 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, triggering the associated location.
- The blue key is rewarded for completing the Chaos Gauntlet, which now appears on the gauntlet menu.
- The green key is found in the first large chest from the Treasure Room, which requires 50 chests to be opened.
- The orange key is found in the chest in the Chamber of Time, which can now be discovered.
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 Demon Guardian as it is revealed to be green, with shoulders, large horns and a toothy smile. It exchanges dialogue before disappearing in a flash of light, leaving a large chest in its place with rewards, including a purple key which unlocks the Demon Gauntlet. Selecting the chest summons the Keymaster, who exchanges additional dialogue, before the chest can be opened.