The Magma Caverns

It appears in the alternative timeline Spirits of Fire.

History
After putting an end to Maj'elka's destruction, the Shrine Maiden and the Traveler venture out to the mountains, where the Necromantic Shamans are poised to rip the world open with a foul ritual. The Maiden orders the Traveler to destroy their minions in order to make the way clear for extinguishing.

The Traveler scours the mazed caverns and disposes of the various flaming undead and gorn they come across. The caves are also inhabited by Soul Furnaces and Infernal Flesh, powerful reanimated dead that can harness the power of fire.