What is "weserburg"

The Weserburg is a modern art museum in Bremen, Germany. Opened in 1991, it is located on the Teerhof peninsula next to the River Weser in an old factory building which was almost completely destroyed in the Second World War. Originally known as "New Museum Weserburg Bremen" (Neues Museum Weserburg Bremen), it was Europe's first "collectors' museum", in that it conserves no permanent collection but mounts changing exhibition of private collections. It is one of the largest modern art museum spaces in Germany.