The castle is home to a rather dry museum on Lublin and Polish history, and a more interesting Gothic Chapel of the Holy Trinity. The chapel dates from the 14th century, and the Byzantine frescoes are the work of a team of Ruthenian painters from 1418. The castle played an important role in Lublin's history. It was the second home of Polish kings during the union with Lithuania, when they would make their trek from Kraków to Vilnius. It was here, too, that the Polish-Lithuanian Union was signed in 1569. Look for the painting The Union of Lublin by the 19th-century master Jan Matejko that depicts the event. The castle was rebuilt in the 19th century in the current neo-Gothic style and served as a prison both under the Tsarist occupation and then later under the Nazis during World War II.