Postojna Cave is a network of 20 kilometres of passages, galleries and chambers into which experienced guides have accompanied more than 31 million visitors in the last 188 years. It is the largest cave in the "classic karst" and the most visited show cave in Europe. In 1872 railway lines were laid in the cave; electricity arrived in 1884.
"Natural phenomena in Bulgaria: Chudnite Mostove (Marvelous Bridges)"
The Marvelous Bridges is a rock formation in the Rhodope Mountains in southern Bulgaria. It is located in the Karst valley of the Erkyupryia River in the Western Rhodopes at 1,450 metres above sea level, at the foot of Persenk Peak.
Two real images:
(images and news by Pabitra Saha)
(information taken from the Wikipedia and Bulgarian National Bank)