Pingos - Drive your players crazy with these earthworks that aren't made by bronze age cultures, ancient astronauts, nor faeries.
Pingos are hills thrown up out of frozen tundra by nothing more than epic frost heave, surrounded by bizarre polygonal land formations, also caused by frost heave (looks like a Voroni diagram).
Check out the pictures, they
really look artificial.
https://en.wikipedia.org/wiki/Pingo
Of course, in your game they
could be artificial. And why not scale it up to the size of a mountain? Inexplicably sitting in the middle of a desolate plain :)