By focusing on three “mosques” in Germany, Özlem Topcu Eralp’s three-part documentary traces the evolution of Turquerie, the fashion for all things Turkish that overtook Europe beginning in the 18th century. The exquisite and unusual Orientalist structure examined in this installment of “A Mosque in Europe” is in fact a pump house constructed in the mid-19th century in Potsdam, the summer capital of the Prussian Kingdom, that served to conceal the mechanical works that provided water to the palace gardens at San Souci.