Largest I've been in
was the Little Neath River Cave system : much smaller than Wookey Hole by a long way, but very scarey none-the-less.
Starts off as a small hole in the side of a river bank and ends up as vast caverns.
(
parlicoot is warm, cuddly and drinking a nice cup of tea,
Mon 14 May 2007, 10:25,
archived)