The subterranean natural treasures, namely the caves of the Aggtelek Karst and the Slovak Karst were inscribed on the UNESCO World Heritage List in 1995.  One of the most endearing treasures of the National Park is the Baradla Cave, which is the biggest and the most magnificent cave in Hungary.  The largest stalactite cave of Europe is situated in this area: the Baradla cave is 26 km long, of which 8 km is in Slovakia, known under the name of Domica. Excavations in and around the cave have proved that it has been a shelter to man for more than 7 000 years. The first written documentation from the caves can be dated back to 1549. Since 1920 it has been used as a tourist attraction. Several of the caves have different specialities. For example, the Peace Cave has a sanatorium which help treating people suffering from asthma.

The variety of formations and the fact that they are concentrated in a restricted area means that the 712 caves currently identified make up a typical temperate-zone karstic system. Because they display an extremely rare combination of tropical and glacial climatic effects, they make it possible to study geological history over tens of millions of years. This exceptional group of 712 caves, recorded at time of inscription, lies under a protected area of 56,651 ha and a larger buffer zone. Today more than 1000 caves are known.