Today’s main attraction will be the spectacular scenery along the Danube, as you cruise a stretch of gorges known as the Iron Gates. Later, head ashore to explore a Paleolithic site and an extraordinarily well-preserved medieval fortress. All along the way, history lines the banks of the river. Keep an eye out for Trajan’s Plaque, which the ancient Romans erected to commemorate the road they anchored in the steep cliffs above the water, and Golubac Castle, built in the 14th century and attacked successively by the Serbs, Magyars, and Turks.