YOU CAN SMELL the sub-tropical heat and humidity. Everyone who enters the Molnár János notices it immediately. It increases with each step into the cave.
Once the sweat starts running down your back, you might wish you were wearing a swimsuit and flip-flops. The source of this extreme heat in the middle of Hungary’s capital city are the thermal springs that heat the highest water level of the flooded part of the cave to 28°C.
As impactful as the first steps into the cave are, the outside is unspectacular. The entrance is close to the Lukáz thermal bath, but there is no sign or advertising, just an old sliding gate behind which you find a small gravel parking area. You wouldn’t guess that it conceals one of the most incredible dive-spots in Europe.
Around an old store, reminiscent of a Turkish bath, a wooden walkway leads into a shaft to the cave, the entrance of which is about 100m into the Buda mountains.
Twin-sets and rebreathers are stacked on long metal tables. Dozens of stage-cylinders lie ready for use. Hundreds of drysuits hang drying.
Stern dark-brown eyes critically consider every newcomer. They belong to Attila Hosszú, whose bald head seems well-matched to his name. Hosszú secured the sole licence from the government to regulate dive operations in the cave, and he alone sets the rules.
Since a diver died in the cave some years ago for unexplained reasons, the government has forbidden any diving being carried out in an uncontrolled way. Hosszú has a number of parameters he has to observe and enforce.
Divers must have at least the Cave Diver Intro certificate; the dive insurance needs to include cave-diving; and enough gas in the form of twin-sets, stages or a rebreather must be available. Each diver must be guided to minimise the risk of taking a wrong turn. “It’s very important to follow all the rules and be able to return home safely,” says Hosszú grimly.
“Attila is actually a very funny guy. On some days he even laughs,” says Zoltan Bauer, one of the guides, digging his elbow into Hosszú’s ribs and eliciting a slight grin from the other man. But if he is in reality the easy-going type, it’s only after the day’s work is over and all the dives have been safely completed.
Hosszú has good reason to take his task seriously. From the entrance the corridors of the cave system extend to 100m deep in many directions, some coming together again, others coming to dead ends. Woe betide those who don’t know the system well enough, and fail to plan their dive properly.
Hosszú and his assistants have now set up to 7km of lines in the caves, but there is still much to discover beyond these.
“For the moment we’ve reached the limits of the dives,” he explains. “After four to five hours, even with rebreathers we can’t go further, unfortunately. The rest of the cave needs even more planning out.”

FOR MONTHS HOSSZÚ AND OTHER experienced cave-divers have been replacing kilometres of previously laid rudimentary lines. “Some were actually just twine,” says Hosszú. Now, in the most important areas, there are decent cave-lines complete with triangular directional arrows always pointing to the nearest exit.
The old entrance, which passed through a narrow shaft, is now to be used only in an emergency or for certain diving profiles. Proper preparations can now be made at the dive-site base, where a plan of the cave is shown on a large white-board as the dive-briefings are given.
The biggest task, however, was to form a 30m-long breakthrough from the main course down to a large pool, to create an ideal starting point for the dives.
A large platform and a massive ladder make entry easier. Large steel nets are suspended from the walls to prevent any sudden rockfall injuring a visitor.
Support is provided for divers who want to go deeper than 40m and on mixed gases. Sofnolime can be pre-ordered, trimix is available and a variety of cylinder set-ups can be rented.
A massive sliding door separates the main passage from the breakthrough to the cave, holding back the heat coming from the system and acting like a gateway to another world.

ONCE YOU HAVE CROSSED THIS threshold there’s no turning back, especially under Attila Hosszú’s expectant eyes. But after the jump into the 28°C water everything else is forgotten, and you can concentrate on the adventure ahead.
The high rocks of the entrance look like a temple of light and shade under the lamps, and beneath us lie the pitch-black depths of Molnár János.
As we start the descent, our eyes seek reference points, and they do become visible after a few metres.
Fine sediment over the rocky walls quickly reveals buoyancy errors, which is why extreme caution is advised while diving close to the walls to avoid the risk of running rapidly into zero vis.
It is vital to stay concentrated and with the guide. Following the exact route is the first requirement, because after a few minutes a direct ascent is no longer possible. From a water depth of 10m you find a thermocline, the temperature dropping to 18-20° to make a longer penetration impossible without a drysuit.
For certain passages a drysuit is prescribed anyway, mainly as an additional buoyancy device.
The expelled air bubbles of the open-circuit divers loosen fine sediment from the roof, and this trickles down through the water. Here the rebreather divers have the advantage, though they need to be experienced to avoid any buoyancy problems.

WE’RE IN A DARK WORLD in which lamps throw their beams to reveal sharp-edged rocks. Around every corner the view initially looks the same and yet soon proves different – there are subtle differences in the sediment and the rock structures.
There are steeple-high cathedrals of stone, the true height of which is revealed only for a fraction of a second in the flash from an underwater camera. Deep columns hint at the distant origins of this cave – Budapest lies on a tectonic-plate gap that has created the long underground passages containing water heated ultimately from the Earth’s core.
“We were able to localise four thermal springs in the Molnár János” says”says Hosszú. “Even if divers are swirling a lot of sediment in a section, it’s gone relatively fast, because the springs have created a slight current that ensures a regular water exchange.”
Which is Hosszú’s favourite section of the cave? he is asked after the dive, as we peel off our drysuits.
“Everywhere,” is the unsatisfactory answer, but after persistent questioning he reveals the truth; he doesn’t want to betray his favourite spots because he is afraid that they would attract too many divers.
It’s not the answer the visitors want to hear, but it’s the right one – every diver can explore Molnár János and choose his or her own preferred place to spend time.
We’re hungry now, and a suitable restaurant is located only about 100m from the cave entrance. Földes Józsi Vendéglje, a far cry from the touristic city places, serves Hungarian goulash, roasted pike-perch and crispy duck, dishes that are delicious and very cheap.
It’s the perfect place to discuss the experiences that have just taken place beneath our feet.
Attila Hosszú is like a different person there, no longer the professional cave-diver concerned only with divers’ safety but a man who laughs heartily as he shares anecdote after anecdote with the visitors to his cave-system.

FACTFILE
GETTING THERE: If you want to take a lot of your own equipment, a long drive is probably required, otherwise fly from the UK to Budapest.
DIVING: Molnár János – note that dive-slots must be reserved, often months in advance, and all qualification and medical paperwork must be in order, www.mjcave.hu/en
ACCOMMODATION: Regnum Residence is a modern hotel near the cave, with “friendly staff but small breakfasts”, says Tobias, www.regnumresidence.hu. Cheaper is the Orion but it’s “a bit old and farther away”.
WHEN TO GO: Any time.
CURRENCY: Hungarian forint.
PRICES: Return flights to Budapest cost from £110. A dive to a maximum depth of 40m costs 70 euros for an individual or 50 euros pp for a group of three. Deeper and longer dives cost 70-170 euros. A “Cave Intro Dive” (not to be confused with the Cave Intro Diver certificate) can be booked for 60 euros.
VISITOR INFORMATION: www.budapest.com