The Halbmondlager was a prisoner-of-war camp in Wünsdorf, Germany, during the First World War.
The camp housed between 4,000 and 5,000 Muslim prisoners of war who had fought for the Allied side. The intended purpose of the camp was to convince detainees to wage jihad against the United Kingdom and France. To that end, "detainees lived in relative luxury and were given everything they needed to practise their faith". It was the site of the first mosque to be built in Germany, a large and ornate wooden structure finished in July 1915.
Wikipedia https://en.wikipedia.org/wiki/Halbmondlager
Address Hauptallee, Wünsdorf 15806, Germany
Coordinates 52°9'55.129" N 13°29'7.731" E