This quest is not available in game.
Archmage Lan'dalock in Dalaran wants you to return with the Artifact from the Nathrezim Homeworld.
This quest may only be completed on Heroic difficulty.
<name>, a friend within the bronze dragonflight has given me information that we must exploit.
The mysterious beings of the Burning Legion called the dreadlords are also known racially as the Nathrezim. Little is known of their homeworld and even that is rumor.
However, it is known that Mal'Ganis of the past has made a critical error: he left behind an artifact from his homeworld!
Through the Caverns of Time, you must travel back to the time known as the Culling of Stratholme. Recover the artifact.