The Cyberden is the base of operations of the Cyborg race, and a map in the original TimeSplitters. Cyberden is an underground hideout with mechanical silos, fans and other industrial ware, and appears to be a (formally) abandoned rocket silo.
In Arcade mode the map is completely accessible, including the two rocket silos, with one having one engine apparently almost falling down into the chamber below. These engines release gusts of steam on occasion, but this causes no damage to players and seems to be purely for effect.
As in Story Mode, there is a console where a lever can be pulled, although in Arcade it has no effect other than changing the screen from red to green.
In this map the sky can only be seen if the player looks up the vent shaft they would be dropped in through in Story Mode; apart from this the map is entirely sealed in.