Centralia, PA has a mine that has been on fire since 1962 and will be on fire for at least another 250 years [0] - the town had to be evacuated in the 80s because it caused people to fall into sinkholes that randomly and suddenly opened up. Scary.
Just drove through there a couple weeks ago. There are basically crevices in the ground exhausting hot humid drafts. Almost uncomfortably hot for a hand, and will fog up glasses.
[0] https://en.m.wikipedia.org/wiki/Centralia_mine_fire