WARNING: THE FOLLOWING GUIDE IS FOR MAGES ONLY. THE REST OF YOU POOR FOOLS ARE FLAT OUT OF LUCK. HAHAHAHAHA!
Welcome to Northrend! Now git yer lazy arse to Dalaran so you can summon all your friends there.
Step one is to nab yourself a self teleport to the place. You need to be level 71. Then you do a relatively simple little quest, and then you’re done. That’s it. No other prerequisites.
At 71, hustle over to Dragonblight (the middle southern zone in Northrend), and head to the place located on the map below.
Alliance mages, you’ll want to head to Stars’ Rest. Horde, head to Agmar’s Hammer. There, you will find an image of an archmage who will give you a quest to attune yourself to the leylines of Northrend.
Once you have the quest, you are heading to the westernmost point on the map shown.
There are lots of minions of the blue dragonflight around, and they will expend a great deal of effort to destroy you. Things called “mage hunters” with all sorts of nasty abilities like frostfire bolt, spell reflects, and mana burns.
The landmark you are looking for is kinda large and sticks out like a naked tauren in ironforge.
Nonetheless, it looks like this:
Directly below that is where you need to be. No need to sneak down there, slipping past mobs. Just bullrush through them, hit Slow Fall, and throw yourself off the edge. They’ll de-aggro soon enough.
Once there, make your way to the sparkly center of the pit. Use the crystal thingy the hologram mage gave you.
At some point, you may need to fight this guy.
He is immune to arcane spells, so you are limited to frost and fire for this fight. He is stunnable, though frost mages will be unable to actively root or slow him, as he is immune to both of those mechanics. However, frostbite procs root him just fine. Slightly over 9k health; a fairly easy kill.
He is on a rapid respawn timer, as there is a quest to kill him. If someone else kills it, you can get the attunement quest done without fighting him.
Anyways. Grab the attunement, grab the portal, zip to Dalaran, snag your level 71 spells.
Did I mention that the only class trainer in Dalaran is a mage class trainer?
Enjoy your port, the envy of your friends, and an entire city built and inhabited by mages, for mages.
Note that this entire process can be skipped if you head to Dalaran by a different means. If, say, another mage portals you there, you can simply go to the trainer, learn the spell, and have no need of doing the quest.
I will frown at you and be disappointed if you go that route, however. Beware. My disappointment knows no bounds.