Back in the 1840s, the "romantic" Frederick Wilhelm IV built a steam pump engine and disguised it in a building designed as a mosque. The steam pump engine was an engineering masterpiece of its time. It was used to pump water from the river into the fountains of Sanssouci.
Once you see Sanssouci's intricate garden and fountain systems, you'll really appreciate the technical marvel behind the engine house. Inside the "mosque" you'll find an exhibition about the building's history.