From The TimeSplitters Wiki

Planet X
Size	Large
Location	An area of Planet X
Climate	None
Unlockable	Completing Story mode up to Cyberden
Recommended Bots	N/A
Recommended Weapons	N/A

For the TS2 Story level see Return to Planet X

Planet X is the biggest map in the series, although it only appears in TS1. There are many cliffside walkways and corridors within the cliffs themselves. One of the most memorable features is the green waterfall near to the main outside part. There are also some evidence of an alien presence, like lamps in the caverns and a hidden alien base.