I had a weird nightmare a few nights ago where there was this perfectly round gaping hole in the ground that was probably a good 15-20 feet across and it was completely dirt/soil inside as though someone had excavated it in the same manner you'd create the hole on a putting green on a golf course just on a much larger scale.
The conditions were that you'd be lowered a good 50 or 100 feet into it (maybe deeper...after all, I was just eyeballing the distance) and you'd be left for dead with the only chance at survival being climbing these crumbly, flat dirt walls that had no textural grips to work with and you were also given no climbing gear either. Also, you had to do this in absolute pitch black darkness. So dark that it stops even looking black as your mind begins to imagine darker shades of brown, blue, or grey in a futile attempt to escape the harrowing grimness of the matter at hand.
On top of all this, there were vermin typical of a sewery ecosystem running about that you would only be able to hear and not see once they shut off the lights.