limestone cave system on the Hungarian-Slovakian border, about 30 miles (50 km) northwest of Miskolc, Hungary, and 40 miles (65 km) southwest of Košice, Slovakia. It is the largest stalactite (stalactite and stalagmite) cave system in Europe, and its stalactite and stalagmite formations are spectacular. The caverns and their surroundings have been designated a national park by both Hungary and Slovakia, and the area was named a UNESCO World Heritage site in 1995.

The caverns were formed in the Tertiary and Quaternary periods in the unevenly uplifted Aggtelek Mountains, which are rich in karstic (karst) features. The subterranean streams are fed by 11 sinkholes. There are more than 14 miles (23 km) of charted pathways. The main path for tourists follows the course of the intermittent Acheron River. There are six entrances to the caverns, three in Slovakia (the Devil's Hole and the natural and man-made entrances at Domica) and three in Hungary (the natural entrance at Aggtelek in the highest cliff face in Hungary and the man-made entrances at Jósvafő and Lake Vörös). The narrow corridors of the caverns connect spacious chambers (with names such as the Black Chamber, the Ballroom, the Hall of Tigers, the Concert Hall, the Banquet Hall, the Room of Lace, the Great Chamber, the Room of Ruins, the Heroes' Chamber, the Reményi Ede Room, Rákóczi's Tent Hall, the Hall of Councils, and the Giants' Hall), and the stalactites and stalagmites, with their diverse colours, shapes, and forms, present a remarkable spectacle. It has attracted tourists since the early 1800s.