After the failed first dives in the lake, the cavers tried to exploring inside the hill. There was the hole which was discovered by János Molnár and his colleagues, and they knew there is water inside but nobody were able to find a passage. In 1959 members of a university cavers’ club descended to the cave and they saw there must be a passage underwater thanks to the low water level.
István Holly and another caver were the first ones, who swam through the siphon with a simple diving mask and a watertight flashlight, without any breathing apparatus. They discovered a room filled with air. István Holly swam through another siphon in the cave. The cavers realized there must be deeper passages in the cave, so they asked the members of a diving club to join them.
During the scuba dives, they found these passages and they descended to 15 meters depth. They saw it would be possible to go deeper as it was an extensive underwater cave system. This was the beginning of the underwater exploration in the Molnár János Cave.
The report about the first swim through the siphon by the freedivers was published in the Egyetemi Lapok, the magazine of the Eötvös Lóránd University Budapest in 1960.
Source: Arcanum Digitális Tudománytár