Considering how powerful it was, it should have looked impressive. There should have been intricate designs engraved into It, you should have been able to look at it and know it was an evil device used for human sacrifice. Instead it was just a simple stone slab with grooves for the blood.
Paradoxically, the longer it was left in the woods, untended, it became more powerful as the laylines beneath it were absorbed with no release. Just one death and all hell would break loose, literally.
It was so far from civilisation though. That couldn't happen.
Until a parachute failed.