Hranice Abyss

Hranice Abyss is a water-filled sinkhole in the eastern part of Moravia, measured so far to a depth of 404 meters (1,325 feet) below the surface. The limestone shaft opens on a wooded slope and leads into a complex underground system of fissures and chambers.

The first written mention was made by physician Tomáš Jordán in 1580, who described unusual gases at the water surface. Geological research began in the twentieth century and led to the discovery of the extraordinary depth through modern robotic divers.

The name comes from the nearby town of Hranice, known since medieval times as a border point between historical regions. Visitors today see a water surface surrounded by rock walls, its stillness occasionally broken by rising gas bubbles.

Access to the cavity is limited to paved paths through forest that shelters the shaft from direct wind. Visitors can reach the upper rim and look down at the water, but should wear sturdy shoes for the uneven terrain.

Specialized remote-controlled underwater vehicles are used for exploration in the lower sections, as human divers cannot reach the extreme depths. Research equipment has documented limestone formations created by thermal springs and chemical processes.