Elector Joseph Clemens began building this castle in 1715. The most conspicuous building on the west end of the Poppelsdorf Allee, it was finished by Clemens' successor Clemens August in the year 1753. The building, which stands on a square plot, reminds one of French and Italian architecture with its four wings and round arched courtyard. Various builders, some of them famous, like Robert de Cotte and Balthasar Neumann, have left their mark here. In 1818 the castle was used to house the natural sciences collection of the university, which is still located there today. Instead of a park, the Botanical Gardens surround the palace, which are particularly worth seeing.