Stalker: Shadow of Chernobyl → Army Warehouses
The Army Warehouses, controlled by the Freedom faction, are a buffer zone between the Bar (Duty) and the Red Forest (controlled by Monolith). Here, you can join one of the organizations and choose a side in the conflict. If you become a Freedom faction, you will no longer be allowed into the Bar without permission, and those who join the Duty faction will have difficulty crossing the border between the Warehouses and the Red Forest—the Freedom faction has a checkpoint there.
Helping the Freedom faction commander repel the Monolith attack is still worthwhile. This will teach you the habits of the stalker cultists. Now let's go through the Radar.