The Dread Citadel - Naxxramas
Archmage Angela Dosantos at Light's Hope Chapel in the Eastern Plaguelands wants 5 Arcane Crystals, 2 Nexus Crystals, 1 Righteous Orb and 60 gold pieces. You must also be Honored with the Argent Dawn.
Arcane Crystal
Nexus Crystal
Righteous OrbDescription
In the thick of Plaguewood lies the entrance to the dread citadel of Naxxramas. Previously, all attempts to enter had been stymied by the magical wards placed upon the rune portal. That is, until now.
We have devised a way to gain entry via arcane cloaking - an old cantrip of the Kirin Tor with a few modifications of my own. Since your dedication to the cause of the Dawn is somewhat lacking, <name>, the price will be high. You may decline and choose to return when you are revered or exalted for a discount.
Progress
None have entered Naxxramas and lived to tell the tale.
Completion
You will feel a slight tingle, <name>. That sensation means it's working. Once complete, you will be able to enter Naxxramas by stepping upon the rune portal in Plaguewood.
Rewards
You will learn: 
Arcane Cloaking
Reputation: Argent Dawn +200