Molnár János thermal cave

Biggest underwater thermal cave in the world

Budapest is the only capital in the world with huge caves and cave systems beneath. The opening of the world’s biggest underwater thermal cave, the Molnár János cave can also be found right in the heart of the city.

The Molnár János cave is a protected area since 1982. The cave system stretches out to more than 5 kms. The cave got its name from the pharmacist Molnár János, who analyzed the waters of the cave back in 1860 and who first supposed that a huge cave system exists underneath.


The Molnár János cave system is located on the Buda side of Budapest, near the Margaret Island. From the outside one can see a small pond (Malom pond) that is filled constantly by the Molnár János spring. This pond was already known back in the Roman Rule, as divers have found Roman constructions at its bottom.

The pond got its name only later, though, from the mills (Malom) the spring was meant to power. Later the Pope donated the pond and the mills to the nuns of the Margaret Island.

Dive explorations

The dive explorations started in the 1950s when the first divers set out to create maps of the Molnár János cave. Since then more than 5 kms were explored. They realized that there are hundreds of thermal water filled halls within the cave, the biggest is over 80 metres long and 16-26 meters wide. The tunnels stretch down to 150-250 metres underground, the furthest down a diver had ever been is 75 metres.

Diving in the Molnár János cave is truly an amazing experience. The water is warm and crystal clear, the limestone walls of the cave have beautiful stone and crystal formations to observe. There are no strong currents anywhere within the cave, actually it moves so slowly that it is difficult even to notice. However, the divers can observe the hot springs that push water out from the ground quite well.

Tragic death of a diver

Unfortunately, the Molnár János cave was closed down in 2011 due to the death of a diver. The death was due to health problems, it was not a diving accident. Since then, we all wait for Molnár János to reopen its gates.

Reopening soon

Our latest information about Molnár János cave is that it will open within the next few months. Preparations and construction work are already done, and we all hope that we can show this magnificient place to interested divers in the near future.

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