Optymistychna Cave

Optymistychna (Ukrainian: Оптимістична: meaning "optimistic") is a gypsum cave located near the Ukrainian village of Korolivka, Borshchiv Raion, Ternopil Oblast. As of 2005[update], it has 230 km of mapped passageways and 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 entire cave lies under a 2 km square area in a layer of Neogene gypsum that is less than 20 m thick. The passages tend to be low and often choked with mud. They comprise a dense network on several levels, making Optymistychna known as a "maze cave".

The cave complex was discovered by the speleologists of the Lviv speleological club "Cyclope" in 1966 who have already studied the complex over 40 years. 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 Ozernaya, 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...