Many maybe don’t even know what kind of geological wonders are hidden under the surface of the capital city of Hungary in Budapest. Early as the roman times this region was already famous about it’s thermal water springs, which was used to establish different well-known baths all around the city. In the 19th century a pharmacist named Molnár János were researching the dry areas of the cave but he knew that there must be a huge water filled cave system as well under the hill. The first underwater explorations began in the 1950’s and continues until today.
The cave today is open to cave divers all year around, and it has until now approximately 6 km of known and mapped passage. The cave tunnels are like a net, and there are many intersections where the divers can make several choices where to turn or make a circuit. Since the water contains a combination of thermal water and cold karst water the water temperature is warm and steady always: it varies between 20-27 degree Celsius. The shallower parts of the cave are the warmer ones, and there is a thermocline in the 9 m area where the temperature changes immediately from 27 to 20 degrees Celsius. Despite of this, the only difference what can be noticed is a slight change in visibility between the two layers of water. There is hardly any noticeable flow in the cave which makes again the conditions less demanding. However, there is an aggressive sediment production in the cave due to the acidic water dissolving the limestone formations. This accumulation of dissolution residue is the reason for some huge room creations inside the cave, but this makes some parts of the cave also very difficult to explore. There is normally no problem with this, on the „busy” passages, where divers travel every day, but unexplored or hard to reach areas remain covered by this silt, and can render exploration typically quite challenging. The best option for many divers is to make a circuit, because even in some of the well-traveled parts of the cave there is a high chance that the way back will have reduced visibility even if everything was done right. The reason for this is the percolation of the sediment from the ceiling and the side walls of the tunnels which is being hit by the exhaust bubbles of the divers. This type of sediment contains very small particles which can stay stirred up for days.
The artificial entrance to the cave has been nicely established by the owner, it is easily accessible and the dive site is well equipped. You can find everything a cave diver needs: many doubles, stages, argon bottles, rental equipment, DPVs, oxygen and any gas fill. Rebreather divers will find as well everything they need. It is possible to use a sidemount system in the cave, but since the passages have plenty of room there is no real need for them. There is also a fully equipped classroom at the end of the hallway, which makes the organization of cave classes very tempting. The divers are receiving a briefing about the logistical aspects of the dive site once they arrive, and after that a briefing about their dive. Every dive is guided by a cave guide who is very knowledgeable about the system, points out potential hazards and knows the most interesting spots like some stone and crystal formations. Although there are a lot of passages, it is not so difficult to orientate yourself, the 6 mm thick lines are well placed, away from the silty bottom, and a big arrow with a given distance always shows the nearest exit.
We believe it is a very lucky and unique thing to have such a cave system in a so easy to reach and well established location. I think many cave divers know that normally how much time and energy is needed to even reach some dive sites while carrying their equipment. Here, the divers just drop an e-mail, send their documents, drive to the entrance of the cave, assemble their gear and they can go diving in a minute. Not only that local cave divers have now a place where they can go together cave diving, the cave is very popular with foreigners too, which is really nice as divers from all around the world meet here and share their experiences.
GUE Quest Magazine Vol. 12, No. 2, Underwater Cave Exploration in Hungray, The Molnar Janos Cave by Zsolt Szilagyi