"For millennia, Ulduar has remained undisturbed by mortals, far away from their concerns and their struggles. Yet since its recent discovery, many have wondered what the structure's original purpose may have been. Some thought it a city built to herald the glory of its makers; some thought it a vault containing innumerable treasures, perhaps even relics of the mighty titans themselves. Such speculations were wrong.
Beyond Ulduar's gates lies no city, no treasure vault, no final answer to the titan's mysteries. All that awaits those who dare set foot in Ulduar is a horror even the titans could not, would not destroy -- an evil they merely... contained.
Beneath ancient Ulduar, the Old God of death lies, whispering.... Tread carefully, or its prison will become your tomb."

- Source http://www.worldofwarcraft.com/info/underdev/3p1/index.xml#ulduartrailer