There's a pine forest near Zernikow, Uckermark district, Brandenburg in Northeastern Germany that had a patch of larch trees that covered 3,600 sqm or 4,300 sq yd. This patch of trees had been carefully arranged to look like a swastika.
While it's unclear how the patch came to be, it's been suggested that it was planted in 1937 by locals to prove their loyalty after a local shop owner was denounced and sent to a concentration camp for listening to the BBC. Another theory is that the Hitler Youth planted it.
Either way, for a few weeks every year during autumn and spring, the color of the larch leaves would change, and contrast with the deep green of the pine forest. The short duration of this color change and the scarcity of private airplanes meant that the swastika went undiscovered until 1992, and it wasn't fully removed until 2000!