The Kostelec nad Černými lesy Castle is the main landmark of the town. The castle was first documented in 1348. Until 1549, when it was destroyed by fire, the castle served as a hunting lodge of Emperor Ferdinand I. After 1550, it was rebuilt in the Renaissance style. After 1750, baroque modifications were made. Today the castle is owned by Czech University of Life Sciences Prague and is used for social and business purposes. The neighbouring Church of Saint Adalbert is connected with the castle by a covered corridor.
Sigmaringen Castle was first mentioned in the year 1077 in the chronicles of Petershausen monastery. The oldest parts of the castle are concealed beneath the alterations made during the 17th and the 19th centuries. The secret of the earliest settlement built on this defendable rock will never be fully revealed: large-scale excavation work would be necessary, which the extensive land development renders impossible. Judging from the many Roman remains unearthed in the area around Sigmaringen, the 12th century keep known as the 'Roman Tower' could be traced back to a Roman predecessor.
The castle remains that have been preserved (gate, great hall and keep) date back to the Staufer period around 1200. The castle remains were integrated into subsequent buildings. The foundations of the castle buildings are to a large extent identical to the surrounding castle wall.
These remains give us a good idea of how the castle might have looked during the 12th century.