From The TimeSplitters Wiki

Site
Size	Medium
Location	Building site with sewer pipes
Climate	Nighttime (TS1) Daytime (TS2)
Unlockable	TS1: "Chinese" on Normal TS2: Beat Story Mode on Hard
Recommended Bots	?
Recommended Weapons	?

The Site map is a large construction site. It is found in TimeSplitters 1 and returns in TimeSplitters 2. The level contains a building under construction where players can stand on girders or break through the glass, a trailer full of pickups, and a pipe system leading to and out of the construction zone.

Site is considered by many to be one of the hardest levels to unlock in TimeSplitters 2, since it is unlocked by beating Story mode on Hard. Many people who own the game have not unlocked the level.