The actual depth remains still unknown — although many divers have attempted to reach the source, which also feeds the Bistrica River — because the water pressure makes it almost impossible to explore the cave’s bottom. The ice-cold water of the blue eye is both mesmerizing and tempting for a lot of visitors. Even though the water’s temperature is 10 degrees Celsius all year, many young people jump right in the middle of the eye, where the spring pushes you immediately to the surface.