Actually it’s not that dark. I mentioned earlier that for various reasons I ended up in the service tunnels of a big retail centre. Its kind what you expect, a bit grungy, very concrete and geographically disorientating.
I went down a working coal mine once. I wish I’d had my camera with me then. There’s always an opp.
I only took a handful of pics, nothing special, but I am quite pleased by the post processing. The following use HDR, Snapseed, TiltShiftFocus, Percolator, King Camera, Dynamic Light & Blender.
There are a few variations on two themes.
adrian4 
Didn’t realise what these were at first. Actually rather wonderful abstracts from underground car park photos. Have to say, Well Done! These are great!