I wouldn't recommend exploring any confined space without gas detector and a sound rescue plan at the very least. Low O2 and/or hydrogen sulphide won't take any prisoners. I've Never been draining, I think the photos look great but having had confined space training in a previous job I would rather let others take the risks and upload the photos for me to enjoy.
Paris makes it a little easier than UK. They mark the interesting ones with a nice parttern. This one is about 60kg, so tricky to open from below, especialy with a 20m drop straignt down and a heavy bag full of wine, cheese and camera equipment.