I would like to refresh my "normal" or Euclidean Geometry quickly and then proceed to Non-Euclidean Geometry. But I don't have a clue where to start. (It's because I want to learn more about Relativity, but my geometry hasn't got an update since long time ago) I don't know what a manifold is, for starters. :) Now I Google about Non-Euclidean Geometry and you got more than 1 type of N.E.G. So, I haven't got a clue where to start. I remember however this kind of a geometry in high school, where two parallel lines cross each other when going to infinity in a point that doesn't really exist? That's as far as my knowledge of geometry goes (I mean, that was the most advanced of "pure geometry" I encountered) So how do I refresh my geometry and get ready for more exotic stuff? I also have no notice from topology, differential geometry or tensor calculus. And what should I do first?