Baradla Cave is a river cave with almost no river in it. The Styx and the Acheron, the streams that dissolved these galleries out of the limestone, now reach the main passage only during floods — a handful of days a year — and otherwise run thirty to forty metres below the walkway. What they left behind is Hungary's longest cave: twenty kilometres of passage that joins the Slovak cave Domica beneath the border, a system of over twenty-five kilometres. Its main corridor runs 6.6 kilometres from Aggtelek to Jósvafő, hung with some of Europe's richest dripstone — the tiered white cones of the Christmas Tree, the domed Minerva's Helmet, pillared halls and flowstone curtains. People came down here long before the lamps: a Bronze Age community used it as a sanctuary around 1200 BC. In 1806 trails, bridges and lamp holders were built for a visiting Habsburg palatine — one of the first caves anywhere fitted out for tourists.
The air holds at about 10°C and near-total humidity whatever the weather outside: the cave breathes cold on your neck in August and feels almost mild in January. Your footsteps follow the old streambed, dry and gravelly, past pools and columns lit one chamber at a time; in the Giants' Hall the lamps give out before the ceiling does. In the Concert Hall, seated for an audience of about seven hundred, choirs and orchestras still perform under the rock. Tours run all year, from an hour-long circuit at the Aggtelek mouth to a through-trip that walks the whole main branch and returns you to daylight beyond the hill. Twenty-one bat species hibernate in the side branches, and archaeologists are still lifting Bronze Age offerings from crevices the route walks past. It has been a UNESCO World Heritage Site, with the Slovak Karst caves across the border, since 1995.