Ziesar features an extraordinarily well preserved medieval castle, which served the bishops of Brandenburg as a residence from the mid-14th to the mid-16th century. With the inception of the reformation, the era of Ziesar as a bishop’s residence came to an end. The castle, however, remained the administrative seat until 1819. It subsequently moved into private hands until it was nationalised after the war in 1945. From the mid-50s to the 1990s, the medieval castle served educational purposes and included a boarding school. Some time later, at the turn of the millennium, reconstruction for today's museum commenced while the castle’s chapel was also restored. Eye-catching are the chapel's prestigious brick front dating from 1470 and its complete painting from around 1500. Tall windows have been installed on the southern front of the chapel, whereas the northern side has no windows, indicating the castle’s defence purpose during the Middle Age.
In the local museum of the state's medieval ecclesiastical and cultural history, a permanent exhibition “Paths to the City of Heaven” features spectacular medieval discoveries such as tracery and curtain murals and two medieval underfloor heating systems. (Museum für brandenburgische Kirchen- und Kulturgeschichte des Mittelalters: “Wege in die Himmelsstadt. Bischof-Glaube-Herrschaft (800-1550)”. The exhibition further visualises the different historic periods of the castle Burg Ziesar on an area of 1,000 square metres, focussing on the many-faceted castle architecture and respective usage during these periods.