The Torre Guevara is the lone remnant of Potenza's medieval castle, a square crenellated tower of dark stone on the highest point of the old town. The castle proper was demolished in the early 19th century; the tower survived by being incorporated into later buildings.
Climb the steps from Piazza Mario Pagano for the view: on a clear day you see the surrounding ridges of the Lucan Apennines stretching to the horizon. The tower interior occasionally hosts small exhibitions.