Artifact

The Artifact is a key item found in Dry Dry Ruins in Paper Mario.

In the area where Mario gets the Super Hammer, the Artifact can be found behind a Stone Block. It can be given to Kolorado at any time and in exchange, Kolorado will give Mario a Star Piece.

It is never actually specified what the origins of the Artifact are. However, it seems to be somehow related to the mystery of Dry Dry Ruins, as mentioned by Kolorado when Mario hands it over to him.