Optymistychna 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.
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