Diros cave, Show cave in Pyrgos Dirou, Laconia, Greece

Diros Cave, also called Glyfada or Vlychada, opens on the western coast of the Mani peninsula at Ormos Dirou, in East Mani municipality. Visitors cross its flooded galleries in narrow blue-white rowboats, numbered like boat 58, that guides pole through tight passages and large chambers beneath dense pale stalactites. A roughly 300 m walkway follows the boat trip.

Locals knew the entrance around 1900, but systematic exploration began in 1949 with Ioannis and Anna Petrocheilos, founders of the Greek Speleological Society. By Ioannis's death in 1960, 1,600 m had been mapped, 1,300 m of them flooded passages. A section opened to visitors in 1961, and by 2005 the surveyed length reached 15,400 m, Greece's longest cave system.

The cave's name alternates between Glyfada and Vlychada. Fossil bones of panther, hyena, lion, deer and rabbit were found inside, along with Europe's largest concentration of hippopotamus bones. Pottery near the natural entrance points to human presence, and 220 m east lies Alepotrypa, a Neolithic cave with rock carvings.

Visitors cover about 2,800 m by boat, a ride of roughly 25 minutes, then continue on foot along a 300 m path. Guides pole the boats through narrow passages and large halls. Air temperature inside ranges from 16 to 19°C, and the water is about 14°C.

The natural entrance is only about half a metre wide and lies just above sea level. Inside, Swiss cave diver Jean-Jacques Bolanz reached a depth of 78 m and still found stalactites at 71 m. Since 2005 the surveyed passages exceed 15,400 m, making Glyfada the longest cave system in Greece.