Here's an interesting video showing the underground world of Wigpool Mine, excellently filmed by Ollie himself, thanks kind sir !
http://www.youtube.com/watch?v=r6JwzaMY4_4

and here's some similar films of Otter Hole

http://www.youtube.com/watch?v=F2mgOU6uEFI
http://www.youtube.com/watch?v=X_c-0olVLxc

Personally I prefer my watersports to be in warm sunshine & clear water with NO chance of getting jammed in a tight crevice !. I have great respect to these tough adventurers and of course the even-braver miners who were there first.