Germany’s first (non functional garden folly) mosque/mesjid is found in the gardens of Schwetzingen Castle[1]. Designed with Moorish-style domes and built in 1780 by French architect Nicolas de Pigage (1723-1796), it is the largest oriental-style building in a German-speaking country. Built from 1779 to 1796, Schwetzingen Mosque is the only 18th century garden mosque still in existence in Europe.
It is a real highlight, set within the Turkish Gardens, in one of the last areas of the beautifully landscaped castle grounds to be completed.
[1] The arts-loving Elector Palatine Carl Theodor extended and transformed his ancestors' hunting castle into a luxurious summer residence, a 'mini Versailles' in the Palatinate near Heidelberg.