Considering the Apart Hotel Vivaldi in Potsdam?
A VT member wrote the following comment about visiting Potsdam:
Steam House by alexberlin
By order of Frederick William IV, Ludwig Persius built a steam engine-house disguised as a mosque on the Neustädter Havelbucht (a bay on the Havel lake) between 1841 and 1843. This finally made it possible to execute the plan made a hundred years earlier to install fountains in Sanssouci Park.