So, to summarise: it ISN'T....
Shute Shelf Cavern
Loxton Cavern
Goughs Cave
GB Cavern
Wookey Hole
Swildon's Hole
Axbridge Ochre Mine
Lionel's Hole
A cave in Hungary
Roman Springs in Bath
Pen Park Hole
St. Cuthbert's Swallet
Charterhouse Cave
Tratman's Temple, Swildon's Hole
- although it could possibly have been any of these, given that it is rather pretty in places and has a lot to offer but many cavers hardly bother to visit it any more..... so where could it be?.....