Optimisticheskaya Cave is the world's largest gypsum karst cave, the total length of which exceeds 201 km, discovered in 1966. It is located near the village of Korolovka, Borshchiv region, Ternopil region. Optimistic's labyrinth system consists of a number of distinct areas. It differs from other caves in a large variety of cave formations, the presence of separate cave horizons. Here, a constant temperature of +11 C is observed throughout the year, relative humidity fluctuates between 84-100%.

This cave is the most attractive for experienced speleologists. A feature of the cave is that there is an increased ionization of air and water, the absolute absence of pathogenic organisms, and recently discovered mineral swamp silt and water. All this makes Optimistnaya a promising object for medical and recreational purposes.