Sampo was maybe the most important thing in Finnish mythology and Finland's national epic, Kalevala. It was a mill that could make money, salt and grain.
Possibly derived from "Sammas/Sampas", the mythological pillar which supported the sky with the North Star as a "nail" on its top and around which the sky turned. The Sampo mentioned in Kalevala was possibly a sacred statue depicting the real Sammas.