From The TimeSplitters Wiki

Last level in TimeSplitters 1. By winning you open challenge mode, and you can open more things too, by winning all difficulties in different times. Like: Lady alien, Warzone level, Spaceways Stewardess, Red Alien and Small heads cheat. In this level, you play as R108 or Gretel. Your mission is to fight your way (or run your way if you want time bonus characters) to the rocket base and find some Goods. They are in left tower, behind the bar table. When you have them, you need to get into rocket, by going to opposite way, to the right tower. You will find some splitters in the way, but, in easy difficult, end is easy. But, in normal and hard, there is minigun turret in the rocket, trying to spoil your good escape. Well, easy way to kill it is you can use Scifi Autorifle plasma bomb, destroying it immediately. Watch out though! If low health, you die too in explosion if you go near it in hurry!