"I don't know what I was expecting, but it wasn't this." -- Unknown
The Sandbox appears as an island beach, surrounded by water, with a gnarled tree growing on it. It is backed by a colorful sunset in a starry, grid-lined sky.
The tree's branches house several doors, each leading to bonus challenge levels. Additionally the island contains a hammock, a stray Process whom Unknown names Luna, and a beach ball. A jukebox can also be found here, and extra music tracks for it can be obtained via the bonus challenges.
Aside from using the doors, Red can ponder the nature of the Sandbox by using the hammock; increase the beachball's number of bounces, play music on the jukebox, and, after the second or third time she visits, send Luna to bark at the ball. The highest branch on the tree has a listed status of "Under Review."
The doors atop the tree branches lead to various bonus challenges that can be completed for more XP and music tracks for the jukebox. Initially only a couple of doors are available, but as the player progresses through the game, more of them will open and become available.
Each door houses a challenge, based around a specific theme (e.g. a Planning Test automatically drops the player into Turn() mode, and tasks them with destroying all Process on the field within that single Turn()). Every challenge completed will award XP and a music track, but it will also close it's corresponding door. However, the door can be re-opened a set number of times throughout the game, with each re-opening unlocking a new challenge. The only exception to this is the door leading to the Practice Test, which always remains open, and is designed so the player can experiment with different Function combos.
It is worth noting that it is practically impossible to unlock all challenge doors within a single playthrough - to unlock all of them would require a second playthrough via Recursion mode.
There are 6 doors to the decayed tree:
- Speed Test - Destroy all Process using certain Functions within the time limit
- Practice Test - A place to relax and experiment on unsuspecting Process in peace
- Stability Test - Survive the Process onslaught using set Functions for a specified amount of time
- Planning Test - Destroy all Process using certain Functions within a single Turn()
- Performance Test - Customise randomly selected Functions and destroy waves of Process
- Agency Test - Face off against a copy of Red with her own Transistor
- Access to Backdoors is granted with the Authenticator Permission, which the user recieves as part of the User Level 4 upgrade after defeating Sybil. The permission reveals hidden Backdoors and allows entry.
- There is a bug that when all tests have been completed, if the performance test was completed last, it will not regain its name and will continue to state 'Access Denied'.
- The solitary, relaxed atmosphere of the Sandbox contrasts with the gregarious persona of Sybil, its creator. However, the presence of Red's songs on the jukebox jibes with Sybil's obsession with her, and a variation of her distinctive umbrella stands at the base of the tree.
- If Red enters the Sandbox whilst the Transistor is under the effects of the Spine, the Transistor will return to normal. However it will fall back under the Spine's effects once Red exits the Sandbox and returns to Cloudbank.