Cave of the Piasa Bird

Origin
According to legend, in the years long before the Europeans arrived in the Meeting of the Great Rivers area, the Piasa (pronounced Pie-a-saw) was a bird-like creature of such great size that it could easily carry off a full grown deer in its talons. But what concerned the Illini tribes of the region was that the creature preferred human flesh. The native people attempted for years to destroy the creature but were unsuccessful and watched with terror as this monster destroyed whole villages. The artifact is the cave in which the pictograph was found.

Effects
The cave can summon the beast; all you have to do is leave a sacrifice in the cave and watch. To bring it back take back the sacrifice.