The caverns of Jeita Grotto, Mount Lebanon are on two levels: the lower caverns are visited by boat over
  a subterranean lake 2000 ft (623 meters) long, while the dry upper gallery can be seen on foot. These caves
  and galleries are known to man since Paleolithic times. The action of water has created cathedral-like vaults
  beneath the wooded hills of Mount Lebanon forming magnificent caverns. The Lebanese speleologists have
  penetrated about 4.5 mils (7 km) from the entry point of the grotto to the far end of the underground river and
  about 1.3 Mile (2.2 km) of the upper galleries.