Lublin Castle sits on the hill at the top of the old town, its tower visible from across the city. The current neo-Gothic structure dates to the early 19th century — the Austrians rebuilt it as a prison, and Nazis later used it for the same purpose — but the hill has had a fortification since the 10th century. Today it houses the National Museum, with collections of Polish painting, decorative art, and silverwork.
The must-see is the Chapel of the Holy Trinity in the castle courtyard, a small Gothic chapel covered floor-to-ceiling in Byzantine-style frescos commissioned by the Polish king in 1418. The art is extraordinarily well-preserved and the combination of Gothic architecture with Ruthenian iconography is unique in Poland. The chapel has limited visiting hours; check in advance.