Optimisticheskaya Cave

Optimisticheskaya Cave, located in Ukraine, is the world's longest gypsum cave, spanning 165 kilometers of passages. Caves are geological formations, and speleology is the scientific study of them. Solution caves, like Optimisticheskaya, are formed by the dissolution of minerals. While most common caves are formed in limestone or dolomite, gypsum caves are created when gypsum rock, which is more soluble than limestone, is dissolved by water. These caves are carved out by water seeping through bedrock, gradually creating passages through chemical action.12