What are your biggest interests?

[the-pi-guy]

I have a friend who is very interested in airplanes, and because of that he knows a lot about airplanes.  He knows how to fix them, how much they cost, knowledge of a variety of planes, and he's learning how to fly them.  

It's pretty cool to have interests that basically drive you to learn everything about those things.  

So what are your big interests that you know everything about?

Or what are your big interests that you wish you knew everything about?