Petrovaradin fortress. One of the largest, most preserved, most complex, counter-mine systems in Europe, beside Terezin and Josefov.

Counter-scarp gallery "Karls Mine" I level (photo: Nenad Šeguljev 2018)

Communicaton gallery II level "Prinz Eugene Mine" (photo: Nenad Šeguljev 2014)

Entrance in IV level "Kaiser Mine" (photo: Nenad Šeguljev 2004)

Communication gallery II level "Leopolds Mine" (photo: Nenad Šeguljev 2004)

First expedition in underground after WWII (photo Branislav Kupusinac 1957)