Optymistychna Cave
 Optymistychna (Ukrainian: Оптимістична: meaning optimistic) is a gypsum cave located near the Ukrainian village of Korolivka Borschiv Raion Ternopil Oblast. As of 2005 it has 230 km of mapped passageways and is the longest cave in Eurasia. Some other sources say it has about 133 miles (214 km) of surveyed passageways making it the fourth-longest cave in the world after Mammoth Cave Jewel Cave and Sistema Ox Bel Ha.