This June 30, 1989 pictorial postmark of Gifhorn, Lower Saxony, Germany shows a windmill. The postmark publicizes Gifhorn's (Pop. 42,000) International Wind- and Watermill Museum.
From wikipedia, "On the Museum's open-air site, which covers an area of around 16 hectares (40 acres), there are currently 16 mills from 12 different countries (as at 2009)."
The panoramic photo of the site shows that the postmark's "in Der Heide" (in the heath/moor) is absolutely correct.