This round tower at the highest point of the city walls was originally built in 1319 as a square tower to protect the landward edge of the city from attack. It was expanded to its current form in 1464 following a design by Juraj Dalmatinac, an architect most famous for building Šibenik's extraordinary cathedral. In TV's Game of Thrones, its exterior doubled as the House of the Undying in Qarth.
The top terrace boasts superb panoramas of the old town and is visited as part of the city walls walk. The lower floor of the fort houses the entrance to the Upper Corner Tower museum.