The Halls of Origination are part of the Titan research facility of Uldum. Along with Ulduar and Uldaman, it was used by the Titans thousands of years ago. Unlike the other two, the Halls' purpose was not to be a prison--it was used for research and development of new races. One of those races was the Tol'vir - a mix between humans and cats, most of which populate the other Uldum dungeon, the Lost City of the Tol'vir, where it is rumored that a deadly secret is hidden.

HoO is a popular dungeon among fresh 85s because of the sheer number of bosses and relatively little trash, as well as the option to skip straight to Rajh, the 'final' boss. It requires level 84 and minimum ilvl 305 to queue up on Normal.

Players who complete Map of the Architects with Tol'vir Hieroglyphic grant the party Map of the Architects--but really, it's a Tol'vir Hieroglyphic, why would you?

From the Blizzard Community site:
Constructed by the great titans, the Halls of Origination are filled with ancient relics and the fearsome guardians that protect them. Rumors abound that the complex also contains a devastating weapon capable of reordering all life on Azeroth. Deathwing has moved to obtain this terrifying device through his agent, Al'Akir the Windlord. Thus far the facility's communication systems have been fully corrupted, but the weapon inside continues to elude Deathwing's grasp.

The sand-filled pyramid is an archaeologist's delight, filled with relics of an earlier age and the fearsome automated defenses that protect them. But a greater treasure is rumored to lie hidden deep within the halls - a secret that could endanger all life on Azeroth.

The armies threatening Uldum know of this secret, and they hope to use it as a weapon. Finding, entering and protecting the Halls of Origination is no longer a matter of academic interest."