Baradla-Domica Cave complex is 21 km (13 mi) long with approximately one fourth of that on the Slovak side and the rest in the Hungary. The first written mention of Baradla cave dates back to 1549 and from 1920 it serves as a tourist attraction. Ján Majko discovered
Domica Cave (Slovak part of the complex) in 1926 and the tourist circuit opened to public in 1932 has more than 1,700 metres (5,600 ft). Cave was inhabited as far as 5000 BC and is an important
archeological site of
Bükk Culture. Temperature in the Slovak part varies between 10 and 12.3 °C (50.0 and 54.1 °F) with a humidity above 95%. see
https://en.wikipedia.org/wiki/Caves_...d_Slovak_Karst
When I was there they had an iron grill at the border to stop people entering the cave on one side of the border and emerging on the other side.