Hranice Abyss, Flooded sinkhole in Hranice, Czech Republic

Hranice Abyss is a steep, elliptical sinkhole about 110 m long and 50 m wide, opening on a wooded slope above the Bečva River. Its dry section drops 69.5 m to the Hranice Lake, and the flooded part has been measured to 450 m, giving a confirmed total depth of 519.5 m without reaching the bottom.

The first recorded attempt to measure the depth dates from 1580. From 1900 to 1902 teacher Václav Šindela lowered a weighted probe from a boat and reached 36 metres. In 1961 Bohumír Kopecký made the first dive with a homemade apparatus; later divers reached 181 metres in 2000, and in 2022 a robot measured 450 metres of the flooded part.

The abyss is sometimes called Macůška, a nickname from before World War II that never caught on. A local legend says the Great Moravian ruler Mojmír II rode his horse into the pit so that his treacherous pursuers would follow him in the dark.

The abyss lies about 500 m from the Teplice nad Bečvou railway station on the Hranice na Moravě–Púchov line, reached by the red hiking mark that follows the Hůrka educational trail. A fence around the rim guards against falls; the pool at the bottom stays in shadow.

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.