Math.
And I like it a lot. >_>; http://i14.photobucket.com/albums/a313/PaiSquared/Calc_surfaces12.jpg
I'm finishing the 3rd and last course on my Calculus textbook, and despite how much I'm not doing that great in it, I'm almost amazed by what we covered. What you might learn in high school calc about derivatives and integrals, that was just in 2D.
I've been thinking, visualizing, and drawing 3D objects. And then! sometimes having to take a 3D object and press it flat to look at it in 2D!
http://i14.photobucket.com/albums/a313/PaiSquared/Calc_surfaces3.jpg
I know I haven't been drawing much, but even sketching simple lines and shapes is