Copying this from my guide of Master. I originally meant to post it on this but oh well. Blame Bethesda for making two similar achievements with almost the same name:
With the Magelight spell, it is easy to cheese Alteration to level 100. Stand outside the solitude gates and face north. Aim at the peak of the mountain. In the right spot, the Magelight illuminates the path all the way up the mountain, easily getting Alteration to 100 in only a matter of minutes.