What is the deepest flooded cave in the world, located in the Czech Republic?

The deepest flooded cave in the world, located in the Czech Republic, is Hranice Abyss. This karst sinkhole lies near the town of Hranice and is partly filled by Hranice Lake.

Its confirmed depth is 519.5 metres: 69.5 metres above the water and 450 metres underwater. A remotely operated vehicle reached the 450-metre underwater depth in 2022, although sediment and dangerous submerged obstacles prevent explorers from reaching the true bottom.

Hranice Abyss is often confused with Pozzo del Merro in Italy, which once held the record for the deepest known flooded chasm. The Czech site surpassed it after later robotic exploration. Researchers also believe the abyss may extend far deeper than its confirmed measurements, but those greater estimates remain geophysical inferences rather than directly explored passages.

The nearby Zbrašov Aragonite Caves are a separate, tourist-accessible cave attraction; they are not another name for Hranice Abyss.