Molten Caves

Molten Caves generates after Deeprock Caverns and only Deeprock Caverns, it generates at high erosion levels, where it is very open with crimson trees and lava, huge pillar/mountainous terrain, and a flat floor.

A screenshot from the Infinity Cave mod, showing molten caves and an uncommon trial spawner.

Structures

Molten Caves may generate 6 structures, 2 which are biome specific, those being the Railway and the Knuckle Trap. The Railway is an elevated structure with a staircase at the middle, where one can get a great overview of the location. The Knuckle Trap contains ancient debris, but be cautious of the trapped ancient debris in the middle. Trial spawners also spawn here.