Passage to Corvus is a dungeon found in the Paths of the Drowned in Act V of Diablo III. Four passages spawn in every game, all accessible from Paths of the Drowned, but only one of them will have access to Ruins of Corvus. The other three will be much shorter and lead to dead-ends, having obelisks to return back.
In order to find the correct passage (unless, of course, player wants to try them all one by one), one must click at least three Nephalem Guidestones, one of which is directly in their path, and two more must be found manually. The swamp contains more than three total beacons, so it's hard to miss them. Each beacon will also grant a free charge of Nephalem Glory.
There are four symbols assigned to passages, one for each: Fire, Wind, Wave and Leaf. Each Beacon eliminates one (the symbol that is eliminated stops glowing). After three beacons, only one (true) symbol will remain.