Zwehrenturm, Gothic tower in Kassel, Germany.

The Zwehrenturm is a stone structure with a rotating dome located at the end of Steinweg street in Kassel's historic center. The building connects directly with the adjacent Museum Fridericianum and now serves as an exhibition space.

Built in 1330 as the southern city gate on the road to Frankfurt, the tower was part of the wall of the Kasseler Freiheit district. After the New Gate opened in 1597, the gate was closed and the tower served as a prison for higher-ranking inmates until the 17th century. In 1709 Landgraf Karl converted it into an observatory with a rotating dome; in 1779 Friedrich II had it linked to the new Fridericianum, replacing the dome with the octagonal observatory room by Simon Louis du Ry.

The tower was transformed into an observatory by Landgraf Karl in the early 18th century, where scholars conducted astronomical observations. Visitors can still discover traces of this scientific use in the exhibition spaces today.

The tower is easily reached from Karl-Bernhardi-Straße in central Kassel and sits near other museums and historic buildings. Visitors should expect some stairs to explore the different levels and exhibition areas.

The rotating dome installed for Landgraf Karl's observatory in 1709 swayed so much that it proved impractical; its turning gear was later moved to the Ottoneum's dome. Since 1997 the tower has been a station of the Laserscape Kassel, with laser beams linking it to the Hercules statue and the Orangery.