In reply to ben b:
It was a good base, dry and comfortable enough with a mat.
Plywood floor and concrete ceiling. There was even a new routes book!
The walls were metal frame covered in polythene. One weekend we took down the old walls and put up new ones with cement and stones that were around the place, we added a window frame (or two?).
I was told that when they replaced the bridge they offered to rebuild the bendy under the new bridge but the National Trust said no.