The Idol of Rygnar is a random quest present in Act II of the Diablo III demo showcased at PAX 2009.
Background
The quest is issued to you after talking to Poltahr, outside the entrance to the Lost Ruins.
The quest requires the player to search through the dungeons of the Lost Ruins to help Poltahr find an item, eponymously named "The Idol of Rygnar".
Reward
You are rewarded with 8400 experience points and an item called "Empire Runners".