Source

Wikipedia (bg): Prohodna

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Статия „Проходна“ (пещера, Карлуково), българска Уикипедия. — cited, not checked by us

https://bg.wikipedia.org/wiki/%D0%9F%D1%80%D0%BE%D1%85%D0%BE%D0%B4%D0%BD%D0%B0

The cave of Prohodna lies in the land of Karlukovo.

Prohodna is a through-cave near Karlukovo, in the Karlukovo karst area.

According to published records two openings in the cave's ceiling are known as “the Eyes of God” (also called “the Spectacles”).