Molnár János-barlang
Hungary's longest active thermal-water cave, opening at the Malom-tó pond on Frankel Leó út in Buda, a few hundred metres from the Danube. More than 6 km of water-filled passages have been mapped, with the deepest sections reaching about 100 m. The upper level is warmed by thermal springs to around 28 °C, while below a thermocline at roughly 10 m the water drops to about 18–20 °C. Fine sediment can quickly ruin visibility near walls and floor, but slow spring flow helps clear it.
Facts
- Region: Hungary – Caves & Mines
- Area: Budapest
- Depth: 0–100 m
- Level: advanced
- Current: low
- Type: cave
- Coordinates: 47.5181319, 19.0359332
- Highlights: thermal water 20–28 °C, thermocline at ~10 m (18–20 °C below), over 6 km of flooded passages, deepest sections ~100 m, large cave lake chamber ~86 × 27 × 15 m, fine silt, guidelines laid by explorers, cave in the middle of Budapest
- Permit: Cave diving requires the consent of the cave's custodian, the Duna–Ipoly National Park Directorate (Nature Conservation Act §51(4); Decree 17/2021 (IV.9.) AM §4 and Annex 4: non-research diving allowed, max 50 persons/day). Consent is issued only for a specific date, to an applicant whose dive leader holds the Hungarian Diving Federation (MBSZ) cave dive-leader and 'cave diver III' (or equivalent international) qualification; the directorate decides within 15 days. In practice individual divers do not apply themselves: dives are organised and guided by the licensed MJ Cave dive center, booked in advance by e-mail (info@mjcave.hu).
- Issuer / contact: Duna–Ipoly National Park Directorate
- Phone: +3613914610
- Email: dinpi@dinpi.hu
- Website: https://www.dunaipoly.hu/
- Tips: Strictly protected cave (fokozottan védett): diving only as a guided dive booked with the single licensed operator (MJ Cave / Molnár János Cave Diving Center); independent dives are not offered. Guided cave dives need at least Cave Diver Intro-level cave certification, cave-diving insurance, adequate gas (twinset/stages/rebreather) and medical paperwork; book well ahead by e-mail. Non-cave divers (at least AOWD, experienced) can only do a short 'cave intro dive' with a guide. A drysuit or thick wetsuit is needed for deeper penetration below the thermocline. Daily cap: max 50 divers/day by law. Prices and opening days change – check current info.