What is infiltration ? Infitration is a MOD for the higly popular Unreal Tournament. I contains a small, but great community. And can be found: HERE

From the developers themself: Infiltration is an immersion into realism, driven by intense military combat, in a squad-based, mission-oriented shooter. Each of those missions brings the distinctive taste of multifaceted warfare in any environment you can imagine. You will choose your gear prior to the mission, based on the kind of soldier you want to be. Decide from a cache of modern-day weapons, keeping in mind the size and weight of the equipment and how much you can carry. Each mission will allow you to become a unique soldier, based on the equipment and skill you contribute to the tasks at hand. *There is more on the website if your intrested*

See urban exploration.