The Eye Of The Earth.
Cetina River source in Mount Dinara Nature Park, Croatia.
This hole of unknown precise depth is said to be apparently more than 300 ft deep. The karst spring is named as such due to its strong resemblance to an eye when seen from above, with varying shades of blue and turquoise. It is the primary source of the Cetina River, the longest river in Dalmatia. The Cetina flows for about 65 miles from the northwestern slopes of Dinara, the highest mountain massif in Croatia standing at 6,000 feet above sea level, until it merges with the Adriatic Sea.