Giant Flaming Pit Of Lava is one of the thirteen network levels in Marathon 2: Durandal.
If you go under the lava (Get 3x health first) there is a rocket launcher and flame thrower. Get out by using one of the under lava side elevators. Once you're out, go get some more 3x health, and slaughter!
Marathon 2: Durandal - Network Level: Giant Flaming Pit Of Lava