|Location||near Ukrainian village of Korolivka, Borschiv Raion, Ternopil Oblast|
|Length||230 km (754593 ft)|
Optymistychna (Ukrainian: Оптимістична: meaning "optimistic") is a gypsum cave located near the Ukrainian village of Korolivka, Borshchiv Raion, Ternopil Oblast. Approximately 230 km of passageways have been mapped within. As a result, it is the longest cave in Eurasia and the fifth-longest cave in the world, after Mammoth Cave, Sistema Sac Actun, Jewel Cave and Sistema Ox Bel Ha. It is also the longest gypsum cave in the world.
The cave complex was discovered by the speleologists of the Lviv speleological club "Cyclope" in 1966. It was entirely unknown before then. There have been more than 50 expeditions since then, but exploration has slowed significantly in recent years, and very little surveying is currently being done. The cave is located very close to the Priest's Grotto or Ozerna Cave, the eleventh-longest cave in the world at 75 miles (122 km), but the two caves have not yet been found to be connected.
In 2008 the cave won the special nomination as a Natural Wonder of Ukraine.
The entire cave lies under a 2 km square area in a layer of Neogene period gypsum that is less than 30 metres (98 ft) thick. The passages tend to be fairly small, no more than 3 metres (10 ft) wide and 1.5 metres (5 ft) tall for most, although at intersections they can be up to 10 metres (33 ft) tall. They are often choked with mud. They comprise a dense network on several levels, making Optymistychna known as a "maze cave".
Optymistychna's gypsum bed is topped with a limestone layer, which has seeped through into the cave via erosion and formed into calcite speleothems. At other places, the gypsum has formed crystals, often tinted a multitude of colors by mineral salts. In some areas, large gypsum rosettes have formed, colored black by Manganese oxide.
- "Optimistic cave. Speleotourism. Active and extreme tourism. Travel.". www.cave-ua.narod.ru. Retrieved 2017-06-28.
- White, William Blaine; Culver, David C. (2012). Encyclopedia of Caves. Academic Press. p. 830. ISBN 9780123838322.
- "OPTYMISTYCHNA IS THE LONGEST CAVE IN UKRAINE - Information Portal Good News". ukrainegoodnews.com. Retrieved 2017-06-28.
- Scheffel, Richard L.; Wernet, Susan J., eds. (1980). Natural Wonders of the World. United States of America: Reader's Digest Association, Inc. p. 282. ISBN 0-89577-087-3.
- Warren, John K. (2016-05-18). Evaporites: A Geological Compendium. Springer. p. 677. ISBN 9783319135120.
|Wikimedia Commons has media related to Optymistychna Cave.|
- Official site of Optimistic cave
- Chapter II.9, Gypsum Karst in the Western Ukraine by Alexander Klimchouk article appearing in: International Journal of Speleology, vol. 25, #3-4, 1996, p. 263-278.