I love this kind of stuff. Not sure I'd want to explore first-hand; I'm a tad claustrophobic.

https://www.newyorker.com/news...e-city-beneath-paris

I was there twice when we lived in Paris. It’s fascinating. IIRC over 200 steps down - and back up.

Thanks for posting this.
One reason I read Les Miserables was for information about the underground Paris.
Will not be going there. Too claustrophobic.
Turned around before I got to the catacombs near Rome.

There was an underground community in early twentieth-century Oklahoma City occupied by Chinese workers. It's inaccessible now (as far as we know) but construction workers uncovered part of it while building the convention center in 1969.

Photos exist from exploration done then, but the city sealed off the entrance within the week, probably to avoid slowing down convention center construction. There is also a health department report from 1921 documenting an inspection saying that the environment down there was "healthy as all get out."

This is the background for my August release, Catacombs, coming soon to bookstores and online retailers near you.

I always get the heebie-jeebies reading about cavers squeezing into narrow passages...