Ruins of Corvus is a zone in Act V of Diablo III. It is accessed from the one (true) Passage to Corvus, and leads to The Great Hall.
As the name suggests, the zone was once the majestic Nephalem city of Corvus. It was eventually rediscovered by Rakkis, though he managed to retrieve very few of the Nephalem secrets.
It is mostly filled with Scarabs and Flesh Golems, but some Enraged Phantasms also can be found within.