A staff member introduces how the Marzahner Bockwindmuehle, a wind mill built in 1993 as a replica of a 19th century mill, works in Berlin, capital of Germany, on May 21, 2018. On Monday, more than 1,100 mills across Germany, historic ones and replicas, had their giant blades turned and grinders powered on to celebrate the 25th German Mills Day. (Xinhua/Shan Yuqi)