The Tapolcai-tavasbarlang — the Lake Cave of Tapolca — runs for several hundred metres beneath the old town. Visitors descend a long flight of stairs into a labyrinth of low-ceilinged passages flooded with crystal-clear karst water. The signature experience is a short row through a series of connecting chambers in a small flat-bottomed boat, ducking under stone arches lit by soft underwater lamps.
The water is a constant 18 to 20 degrees and the cave a humid 17 — a relief on a hot summer day. Visits are timed; in high season expect to queue. Allow 45 minutes for the full tour. The cave's microclimate is also used therapeutically for respiratory disorders, with a separate clinic at street level.