Smederevo Fortress in City of Smederevo

You're standing at Smederevo Fortress, one of the largest fortifications in Southeast Europe. Look along those walls. Together they run for a kilometre and a half, more than two metres thick and topped with battlements. Twenty-five towers rise along them, each about twenty-five metres tall. The fortress sits on a triangular plain where the Jezava river flows into the Danube. Because it was completely surrounded by water, it's classed as a water fortress.