Where is the world’s deepest underwater cave?

Hranice Abyss, in the Czech Republic, is known as the deepest flooded cave system on Earth. Divers and probes have explored it to great depths, and the full bottom has not yet been reached. The system is notable because the air-filled entrance shaft is much shallower than the submerged passages below. Scientists study it to understand karst geology and subterranean water systems. Its exact maximum depth remains a subject of ongoing exploration, but it is recognized as the deepest known underwater cave environment.