[@BCTheEntity]
Accepted! The lava would actually be further down in the cave systems.
o3o b

Damn, you guys are really thinking about this! They aren't frozen, yet, and determination should be keeping them plenty warm! I mean, think about Frisk running around after leaving the ruins! (Then again, this could be a final hallucination before they freeze to death, the monsters not at all being real...theory theory theory theory theo-)

Shoulda mentioned, but there is a dark cave, and there is a crevice with their source of light, where the cooler air is leaking from.