Ružica Church is a small Serbian Orthodox church built into the walls of Kalemegdan fortress, accessed through the lower fortifications. It occupies a 14th-century gunpowder storage room converted to a place of worship, and is one of the few surviving medieval religious spaces in Belgrade — a city that has been destroyed and rebuilt so many times that medieval fabric of any kind is rare.
The interior is intimate and dark, lit by the famous chandeliers of repurposed weapons. Two large sculptures of medieval Serbian knights stand guard at the entrance. The church is still active — services are held regularly — and can be visited between services. The adjacent spring and small courtyard give it a remarkable sense of quiet, given that it sits inside what is now one of the busiest parks in the city.