Molvanîa is a small land-locked country located in eastern Europe. So far not part of the European Community the land is still very poor, but also pretty exotic and considered to be probably the most intense travel experience remaining in Europe. There is a pretty good guidebook by jetlag travel guides which is published in many languages.
The underground tourist sights are still pretty rare. The country has numerous karst areas in the Molvanîan Alps, also numerous subterranea, but very few are accessible as tourist sites by now.