I run two marathons a year. My training consists of running home from work in Berlin during the week and taking off early in the morning on weekends, which means until April, all these runs are in the dark, after that, in the light, but always through the heart and suburbs of Berlin listening to podcasts and snapping pictures with my cell phone. You may also be looking for my other marathon sites from 2006, 2007, or 2008, or check out some of my other projects.
If you have never run a marathon but think you might want to, just sign up for one and then start running 2 or 3 times a week. Just do it.