Budapest
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Every day, crowds thrive on Budapest’s Lukax thermal bass, with yellow trams rattling along Frankelleo Street. There is little doubt that there is a hidden world away just outside the yards below the city’s historic streets.
From the entrance at the foot of Roz Sadom, at the foot of Roz Sadom, a wealthy area of elegant villas and tree-lined paths, Mornal Janos’ caves extend over 3.6 miles (5.8 km) and are soaked close to 300 feet (90 meters) below the surface. Clear water gets flooded with warm bath temperatures, one of the world’s largest active hydrothermal caves, and one of the rare things open to certified cave divers.
The path to the cave is easy to overlook from the streets. Next to rocky limestone cliffs, a small lake covered in lilies and algae shines beside a crumbling 19th-century building resembling an Ottoman bathhouse. On the firewall next to it, the diver’s mural suggests the following secrets:
Through a gate that passes through an old bathhouse, once one of Hungary’s first concrete structures, the narrow alley leads to a cliff-markless doorway. On top of that, the sign reads “Happiness Factory” and is adjacent to the emoji smile. As you enter the brick entrance, the temperature rises with geothermal heat. Diving gear lined up in the hallway. Finally, behind the painted curtains, a staircase falls into a rocky entrance, where black water awaits in the darkness. Here, divers step into the warm water, their headlamps thrust into the darkness, descending into a quiet, sparkling world.
Budapest is famous for its gorgeous baths and spas, but its hot water does more than just relieve the muscles and relieve illness. For thousands of years, the same geothermal activity that supplies urban baths carved a network of over 200 caves beneath the streets as the mineral-rich springs slowly dissolved into the surrounding limestone, Marlestone and Karstlock.
Molnár János is still alive and growing. Hydrogen sulfide and carbon dioxide rich water keeps rocks infiltrated and creates mildly acidic cocktails that eat walls. The result was a maze of Swiss cheese in the Chamber of Commerce and the aisle.
“It’s very rare that there are hot water caves,” explains CsabaGőcze, a dive guide at MJ Cave, a local operator who offers guided cave diving. “Usually, cave diving means water between 4-15 degrees Celsius (39-59 degrees Fahrenheit), where it’s 27°C (80°F) above.”
Warmth drops to 27°C, 20°C (68°F) on the surface, and cold water from Buda hills drops to 17-18°C (62-64°F) as cold water below. Some of the cave’s water is still fed to nearby Lukax baths via underground pipes, but stone steps plunging into the water rerouted the original entrance, making it easy for divers to access.
Molnár János surprises many first-time visitors. Unlike the tight and twisted passages of other caves, it offers spacious rooms and gentle flow.
“It’s absolutely gorgeous,” says Csaba. “Great, open space and very few restrictions. This is a relatively easy dive. If properly trained.”
That training is essential. Only certified cave divers are permitted. Experience of complete darkness and vulnerable environmental demand. The water is completely clear until someone polishes the sides of the cave, or disturbs the soft bottom and swirls fine silt particles into the beams of the headlamp.
“Usually you can see it until the torchlight arrives,” says Csaba. “But when people touch a wall or kick the silt at the bottom of the aisle, their vision drops very quickly.”
To prevent this, divers follow meter-stretched guidelines on the cave floor to ensure that the water remains pristine. Their attention is rewarded with a tour of surreal landscapes: mineral striped walls scattered with crystals, chambers that change color, and textures as follows.
“Some locations in the cave look completely different because there are areas with coloured rocks, areas with crystals and areas without them,” says Csaba. “The best dives are where you go through some of these areas, so experience them all.”
Shrimp – invisible – darts in the light. The remains of the Panonian Sea that covered much of modern Hungary millions of years ago, fossilized shells and sea wichin still cling to the walls.
Science and Adventure
The cave has not yet been fully explored. The officially mapped network is 3.6 miles, but new passages are regularly found. Volunteer explorers take weekly expeditions in the caves, take measurements, lay new lines and update maps that have not yet been published.
“The official map says it’s about 5,800 meters, but there’s a lineless corridor,” explains Csaba. “Some people don’t lead anywhere, but others may be part of something bigger.” He believes the cave can extend up to five miles.
Researchers also collect water samples, monitor microplastics, and collect signs of contamination. A 2022 study detected some contamination at known interfering sites in the cave, but the recently explored areas remain untouched and untouched.
For certified cave divers, taking part in a diving here is very easy. MJ Cave will perform morning dives on reservations. After briefing and gear setup, the first hour of dive follows key guidelines and then deeper exploration of options. Some dives reach approximately 200 feet (60 meters) and require a decompression stop.
Traveling to Hungary without equipment is not a problem. Full Gear Rental is available on-site.
