Baradla Domica cave system, Karst cave system in Aggtelek and Kečovo, Hungary and Slovakia

The Baradla-Domica cave system is a 25.5-kilometre network of passages in Triassic limestone, linking the Baradla cave in Hungary with the 5.3-kilometre Domica cave in Slovakia. Its main branch runs seven kilometres from Aggtelek to Jósvafő, averaging 10 metres wide and 7–8 metres high, and widens into large chambers. The photograph shows a bare rock chamber with long pale-tipped stalactites, banded brown and cream walls, rounded stalagmites and a shallow dark pool.

The cave first appeared in written records in 1549 and underwent systematic exploration in the late 1700s when initial surveys began mapping its passages. These early expeditions revealed the vast scale of the underground network beneath the region.

The cave's natural entrance has been open since prehistoric times and sheltered Neolithic people. The Acheron stream, named after the Greek river of the underworld, flows through the main passage only during floods; the Styx stream arrives from the Slovak Domica side. Visitors walk the main path along the Acheron's dry bed.

Guided tours operate daily through lit sections of the cave, with established routes and railings ensuring visitor safety as you move through the passages. The terrain is generally easy to navigate, but bringing comfortable footwear and a light jacket is wise since the underground air stays cool throughout the year.

The Acheron stream, which carved the main passage, now flows through it only during floods; in dry periods it drops through sinkholes into the Lower Caves 30–40 metres below. The stream is fed by eleven dolines, and the system's catchment area exceeds 40 km².