Prohodna

Prohodna is a karst cave in north central Bulgaria, located in the Iskar Gorge near the village of Karlukovo in Lukovit Municipality, Lovech Province. The cave is known for the two eye-like holes in its ceiling, known as God's eyes.

Prohodna is the best known attraction in the Karlukovo Gorge, one of the largest karst regions in Bulgaria and a popular location for speleology. Formed during the Quaternary, Prohodna is 262 metres long, which makes it the longest cave passage in Bulgaria. The cave has two entrances which lie opposite one another, known respectively as the Small Entrance and the Big Entrance.

Source: Wikipedia