The Einsteinturm (Einstein Tower) on the Telegrafenberg south of Potsdam city centre is one of the most important buildings of 20th-century Expressionist architecture — a solar observatory designed by Erich Mendelsohn in 1920 to test aspects of Einstein's theory of relativity. The building's curved, flowing form looks sculptural rather than functional, with organic shapes that seem to anticipate the Bauhaus and mid-century modernism simultaneously.
The tower is still a working astronomical telescope, operated by the Leibniz Institute for Astrophysics, which means access is limited. Guided tours of the Telegrafenberg science campus (which also includes several 19th-century observatories) run on Saturdays and include the exterior of the tower; interior visits are possible on special open days. The campus itself is attractive — a collection of observatory domes and scientific buildings on a wooded hill above the city — and the walk up from the train station takes about twenty minutes.