about 5 or 6 of us spent 6 weekends at nant ddu in 2006 draining the deep adit to the north east, after a stupid amount of digging and pumping through the nite we lowered the water enough to access the deeep adit through its air shaft, the water was still up to our chins , David and i made it as far as a huge collapse under another supposed blocked adit but not to the shaft, i wrote a report on our findings , ill see if i can dig a copy out or at least photocopy it for you, there are another 3 adits to dig there that i never got back to, one from memory is supposed to be very long, the joy of this mine is you can get the truck right to it, i wouldnt advise going down the main shaft , a hell of a lot of stuff has slid down there and the ground at the collar is very unstable:)