How random? What's rubbish? One man's trash is another man's treasure! It could still be anythingggggggggggggggg! My theory, Erwin Schrödinger is in there with a jar of acid.
It's a NNNEEEWWW CCCAAAAAAAARRRRRR! // Said in my best impersonation of the Price is Right announcer.
Considering this is Clockwork Empires it'll probably be more like that Se7evn movie. "Whats in the box? Whats in the box!"
An actual human head would be anticlimactic; we have plenty of those lying around all over the place already.
I found one of these also on a cliff. I approached it carefully, risking only a naturalist. "The box... you opened it, we came." But it wasn't that. Yet. Soon
That box will shelter one (1) wayward drunkard after devs add severe consequences caused by binge drinking.