Well of Barhout ("Well of Hell") in Al-Mahra, Yemen

[Astronuc]

Another interesting and unique feature on the Earth's surface is the Well of Barhout. It is described as a sink hole, but looks more like a cavern, in the middle of the desert. https://en.wikipedia.org/wiki/Well_of_Barhout
Location: Al-Mahra, near Hadhramaut, Yemen
Coordinates: 17°20′25″N, 52°26′38″E
Depth: 100–200 m (330–660 ft)
Length: 30 m (98 ft)
https://en.wikipedia.org/wiki/Hadhramaut

Apparently, there are noxious gases emanating from the cavern and little oxygen in the depths. Origins are unknown/uncertainty.

The Smithsonian Volcanic Program reports an old volcanic field in Hadhramaut region. https://volcano.si.edu/volcano.cfm?vn=231180
The last eruption is unknown, so perhaps it was prehistoric.

https://phys.org/news/2021-06-danger-demons-yemen-mysterious-hell.html
https://news.yahoo.com/well-hell-gaping-desert-hole-122159139.html
https://www.france24.com/en/live-news/20210621-danger-and-demons-yemen-s-mysterious-well-of-hell

Maybe an extinct volcano?

 

[anorlunda]

It is described as a sink hole, but looks more like a cavern, in the middle of the desert.

Sink holes are often caused by collapsed caverns.