Örtze is a river of Lower Saxony, Germany. The Örtze rises north of Munster in the Große Heide and, after 62 kilometres (39 mi), joins the Aller southeast of Winsen.

Munster, also called Munster (Örtze) or formerly Munsterlager, is a small town in the district of Heidekreis, in Lower Saxony, Germany almost equidistant from Hamburg and Hanover. The town is home to the German Army's largest garrison and is situated between the two training areas of Munster North and Munster South. It is also the fourth largest garrison in the German Armed Forces. The German Chemical Defence Research Establishment and the Society for the disposal of chemical warfare agents and old armaments GmbH (Ltd.) (GEKA) are located in Munster.