Metro 2033 by Dmitry Glukhovsky
Twenty years after the nuclear war people live underground in the Moscow metro. Each station is it's own and we follow Artyom as he travels from his home at the station VDNKh to group of stations that form the city Polis. He goes there to get help for his home station that is under attack from the dark ones, mutants with psychic powers from the surface. As he travels he meet the factions like the Soviets and the Nazis that has formed in the metro and some help him and some try to kill him. Soon he begins to believe that this journey is his fate and that something is helping him from the shadows of the metro tunnels.
Epic book =).