When you can reach the Greybeards at High Hrothgar you can level up your sneak skill in a very easy way. All you have to do is sneak behind one of the Greybeards and wait untill you become undetected. Then all you have to do is attack them and then repeat the Greybeards will not attack you in anyway and this is not a crime. You can use a weapon but you have the risk of killing them it works fine while unarmed.