Go to http://www.siteo.net
, aplace for fortifications all over the world, there is a link of a german club visiting bunkers of all kind and all ages in Germany and outside, and there is a report about a visit to the Mareth line (in german lenguage) with photos. This line is just in military use, a fact that was new to me. Sorry, but I have name and link of these fellows not at hand.
HTH - Iwailo