Azvor Koba is a nature reserve declared in 1963 with an area of 10 hectares, which includes the Koba River, which is one of the many unsolved karst mysteries and one of the strongest and deepest Croatian springs. This natural mass of green, turquoise and blue lake will enchant you with its picturesque appearance, and the upper flow of the Cuba River, thanks to its wealth of flora and fauna, is called the Enchanted Butterfly Valley.