There is a book ... well quite a few books actually. Here is one I can recommend:
H?HLENF?HRER SCHW?BISCHE ALB / H?hlen, Quellen and Wasserf?lle by Hans Binder and Herbert Jantschke 2003 288 pp, 74 illustrations which include 19 maps in colour, 20 drawings and 35 colour photographs. The book is the 7th edition and is a handy guide to the caves of the Swabian Alb in the south western corner of Germany. The longest cave is over 6 km long! SB In German.
Hopefully, one of the Mendip clubs will have a copy in their library.