Beats Wookey Hole into a cocked hat eh?
Or even the Blue John caves in Derbyshire.
I think the fact you have abseil 260ft down to the cave entrance rules me out visiting, I not exactly mad keen on heights.
A thought: If you have to abseil 260 down, how do you get back up again? Could there be a whole tribe of stranded tourists living at the back of this cave?