I went to this mine 3 weeks ago (Mina El Eden in Zacatecas, Mexico). Not the same as a natural cave, but still very dark and easy to bump your head against rocks.
It had lots of interesting-looking shiny minerals, an underground river, and several statues of half-naked miners. Supposedly, back when it first started getting used in the 17th century, it was a series of narrow passages with no stairs that miners had to climb their way back up, carrying everything they'd found on their backs, to get out, where they could often come across toxic gasses.
The pictures I took look extremely dark, so I decided to use a randomly picked one I found through Google instead.
