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The Deepest Underwater Cave is in the Czech Republic, and its Bottom Hasn’t Been Found Yet

Krzysztof Starnawski first dived in the cave 20 years ago. Now, he led the team that found that “Hranice Abyss” is the world’s deepest underwater cave. Credit: Marcin Jamkowski/National Geographic
Krzysztof Starnawski first dived in the cave 20 years ago. Now, he led the team that found that “Hranice Abyss” is the world’s deepest underwater cave. Credit: Marcin Jamkowski/National Geographic




The deepest underwater cave in the world seems to be in the Czech Republic. This is a flooded limestone chamber called Hranicka Propast, or Hranice Abyss, located in the eastern part of the Czech Republic. The Czech Speleological Society claims the cave to be at least 404 meters deep, dough, in reality, nobody knows just how deep it actually is.

The team was led by Polish explorer Krzysztof Starnawski. In 2015, he took a dive within the deepest pool in the world nd passed through a narrow slot in the underwater cave. He was able to reach a depth of 265 meters, before being forced to resurface. But at this depth, he wasn’t able to see the bottom, even though he had to spend six hours in a decompression chamber after he resurfaced. Starnawski then decided to use a remotely operated underwater robot (ROV) in order to be able to reach those incredible depths of the Hranice Abyss.

First diving to about 200 meters they released the robot  which descended another 204 meters – the full length of its cord. And even if the ROV went as deep as it could, it too wasn’t able to take a glimpse of the cave’s bottom.

The control panel of the ROV. Credit: Krzysztof Starnawski Expedition
The control panel of the ROV. Credit: Krzysztof Starnawski Expedition

“During this push, the most important part of the job was done by the robot,” he said.

“I scuba dived down to 200 metres just before the ROV’s deployment to put in the new line for the robot to follow.

“The goal was to give the ROV a good start from there to the deepest part of the cave.

“The results were astonishing,” he added.

Even so, Hranicka Propast beat the previous record holder, a flooded sinkhole in Italy called Pozzo del Merro, by 12 meters. The team plan of exploring the Czech cave even further, of course, by using a longer cord this time around. National Geographic was the first to report this story and was also partially responsible for the funding.

Schematic showing the various pathways and crevices of the Hranicka Propast cave. It ends with “???” because they’ve yet to map the bottom. Credit: Krzysztof Starnawski / Facebook
Schematic showing the various pathways and crevices of the Hranicka Propast cave. Credit: Krzysztof Starnawski / Facebook