Prohodna is a cave in north central Bulgaria, popular tourist attraction for the two eye-like holes in its ceiling that create an eerie effect. Prohodna is 262 meters (860 ft) long, and has two entrances which lie opposite one another, known respectively as the Small Entrance and the Big Entrance. The cave owes its name, which literally means Thoroughfare Cave or Passage Cave, to this feature. Prohodna is most notable for the two equal-sized holes in the ceiling of its middle chamber. The holes, formed through erosion, let in light into the cave and are locally known as the Eyes of God or Oknata.
Prohodna cave entrance (Kaloyan Karaivanov/ CC BY SA 4.0 )