Once you reach about level 20 or so, and have healing restoration ability, you should be able to utilize this method. Approach a giant (without a companion) and try to coax him away from any other giants or mammoths that might be near him. Do this by approaching him until he raises his club, and then slowly take a few steps backwards until you have him isolated from the rest of his friends. Use your shield to block his blows and heal yourself as necessary. Do not strike him back, just protect yourself. You may have to run away occasionally, to regenerate stamina and then immediately return and allow him to pummel you again. Once you have the perk to heal health AND stamina, this process will go quickly. Your block level with rise quickly, as well as your overall level. (Restoration will also rise, although slowly.) Once you reach 100 block, make the ability legendary, and repeat the process. You will rise in levels very quickly, as well as obtain a lot of perks, that you can apply anywhere you want! Keep in mind that when you level up your character, your emenies level up as well! You want to maintain a balance and basically use this for a much needed perk point. I don't recommend doing this strictly to level up until you are at a much higher level in the game.

I don't get the draw for power leveling. It's way more fun to level up at the pace of your adventuring.