My dad opened me up to riding single-tracks and I've loved it. Since then, I've been doing more and more intense mountain rides. Also, moving through tons of snow and slush with ease on my mountain bike was tons of fun. Probably because I've always felt hindered by the snow in a road bike/fixed gear.
I used to ride an old Myata seven ten, and I get to ride it every time I'm at my parents' house. It's a fun bike. My latest fix is cyclocross and long distance riding.