Tilkiler Cave, a.k.a. Tilkiler Sinkhole, (Turkish: Tilkiler Mağarası a.k.a. Tilkiler Düdeni) is a cave located in Manavgat district of Antalya in southern Turkey. It is named after the nearby village Tilkiler.
It is situated east of Tilkiler village and about 4 km (2.5 mi) northwest of Oymapınar Dam at 150 m (490 ft) above sea level. The distance from Manavgat is about 20 km (12 mi). Tilkiler Cave was discovered in 1976 during the preparatory construction works at Oymapınar Dam while excavating an injection gallery. The horizontal developed cave has a length of 6,650 m (21,820 ft) and is 159 m (522 ft) deep. It is the country's third longest one.
The cave was constituted in the Miocene conglomerate rock formation. It is also partly formed in limestone. These characteristics make it valuable for scientific research. The ponds inside the cave are at different elevations. Water level varies between summer and winter ranging between 68 and 128 m (223 and 420 ft). The cave floods in springtime. A few kilometers far from the entrance, there is a hall, where the ground is completely covered with sand. In 1977, French speleologists built there four small sand castles that gave the hall the name "Hall of Castles". It was observed 27 years later that the sand castles were still intact.
Source(except map and map visuals): wikipedia.org