Prohodna (Bulgarian: Проходна) is a karst cave in north central Bulgaria, located in the Iskar Gorge near the village of Karlukovo in Lukovit Municipality, Lovech Province.

Prohodna is the best known attraction in the Karlukovo Gorge (part of the Geological Park Iskar-Panega), one of the largest karst regions in Bulgaria and a popular location for speleology.

[1] Formed during the Quaternary, Prohodna is 262 metres (860 ft) long, which makes it the longest cave passage in Bulgaria.

[3] The size of the Big Entrance of Prohodna makes it suitable for bungee jumping[4][circular reference], and it is among the popular spots in Bulgaria for that activity.

The phenomenon was featured in the 1988 Bulgarian film Time of Violence;[6] in the scene, a priest named Aligorko prays below the Eyes.