Legacy: "Courtyard Stronghold"
Scenario: K'tharn summons you and tells you that the power source for the portals is threatened by the Skaarj. He has sent you to protect it and then to find your way back to the Nexus.

Afterwards, it is probably best to simply open the other doors yourself to prevent unwanted intrusions into the inner courtyard.
Courtyard 2: If you are wondering what you need to do after the source has been secured, look around outside a little bit, then return to the inner courtyard after you have changed something.

New Weapons and Significant Items: Sniper Railgun, Sticky Bombs, Nali Ruby, Detonator Pack, Warp Key
Destination at End of Level: The Nexus, only about a few yards from where you were originally standing.