I was exploring the Paris catacombs a couple of years ago and we bumped into a group of young "cataphiles", who seemed friendly enough when we met them, but then immediately proceeded to let off a smoke bomb in a crawley passage which accesses a closed section in one of the former quarries. I know it's closed because we did every inch of it trying to find an alternative way out. Even 40 minutes later, with very limited airflow, the section was still filled with dense smoke. We did manage to find a way through (obviously) by going slowly and feeling for the polished path but it wasn't a huge amount of fun.
I don't like the look of that woodwork.