Where is the largest underground lake?

The Dragons Breath Cave in Namibia contains what is often described as the largest known underground lake not covered by a glacier, with a surface area of around two hectares far below the surface. In the United States, the Lost Sea in Tennessee is one of the largest underground lakes open to tourists, who can explore it by boat. Underground lakes form when water collects in caves and caverns, often in limestone regions shaped by slowly dissolving rock. These hidden waters can host unusual life adapted to permanent darkness. Their full extent is often unknown because much lies beyond explored passages.