It's A War Out There 2 (2011)

Caleb finds an axe zombie carelessly wandering around a cliff-face, falling to its death. Caleb figures this must herald a nearby Cabal stronghold, and so he decides to check it out, again to relieve his endless boredom. First he comes across an old library, which he blasts through, before retreating down into the sewers, and again through a laboratory, finding a similar portal that leads out into a lava temple. There he has a surprise encounter with Tchernobog, whom he defeats before once again heading along his way.