So JamP0und32's solution is a great way to do it, but if your like me and don't feel like crafting the gear and having the right enchanting levels and potions and what not, save this for last. So on to how I did it relatively similar:
>Finish the Dragonborn DLC where we will be looking for a specific black book.
NOTE: You will need 11k gold, but by this time if you finished mostly everything else should have well enough.>Go South East of Raven Rock to Kolbjorn Barrow
Map:
http://elderscrolls.wikia.com/wiki/Kolbjorn_Barrow_(Dragonbo...)
>Talk to Ralis Sedarys at Kolbjorn Barrow to start the Unearthed Quest.
>First time you talk to Ralis Sedarys, he will ask for 1000 gold to get some miners. You must then wait 4 days. What I did was just go back to Raven Rock and wait 4 days. A courier should show up to deliver a message to continue the quest. If he doesnt show up, just fast travel somewhere then back to load him in.
>When you visit, you'll discover all the miners are dead and there is a draugr problem. Once they are all cleared out, Ralis will ask for 2000 gold this time.
Essentially you do this 4 times each with a unique problem, first is 1000, then 2000, then 3000, then 5000.
>After waiting 4 days after paying 5000 gold, you'll follow the marker down to a deeper part of the ruins where a dragon priest will raise and must be defeated. After defeating him you have access to the Black Book: Filament and Filigree.
>When done with the Black Book, take the Secret of Arcana power which will allow you to use spells for no mana cost for 30 seconds.
>Head to Redwater Den where you can find a Spell Tome: Telekinesis in a cell with a dead NPC.
Map:
>Now you got everything you need. Head to Windhelm or Markarth and keep fast traveling to each location when using the spell to go straight to lvl 100 Alteration. Drop an item down, (I used Clay, anything in Misc inventory should do fine) and equip Telekinesis on either
or
. Equip Secret of Arcana and press
. Use the telekinesis ability and then go to your map and fast travel to opposite city across the map. Now wait 4 hours and repeat the steps until you are at a desired level!
Hope this helps as I found this to be much easier!
Edit: I should note that I hit level 78 and went to all the dragon peaks / dragon symbols on the map to find a legendary. I ultimately found mine though in Arcwind Point
Edit2: As Orgaz put it, you do need to remember to make the 100 skill legendary so it resets to repeat the process