Brocken spectre

A Brocken spectre occurs when a person stands at a high altitude in the mountains and sees his shadow cast on a cloud at a lower altitude.

From Wikipedia:

The phenomenon can appear on any misty mountainside or cloud bank, even when seen from an aeroplane, but the frequent fogs and low-altitude accessibility of the Brocken, a peak in Germany's Harz Mountains, have created a local legend from which the phenomenon draws its name.

The Brocken spectre was observed and described by Johann Silberschlag in 1780, and has since been recorded often in literature about the region.