In episode 224 of Phedippidations, Steve re-introduces the audience to the idea that perhaps one day, he would like to run an ultramarathon (defined as any race over 26.2 miles in duration). As he points out the most common distances in this class of running are 50 and 100 either miles or kilometers.
Now, my wife has always thought it would be cool for me to do one of these races one day. Usually when she mentions it, I point out how much time away I already have to spend when I am in marathon training mode, and clearly that would be WAAAY more if I was training for an ultra.
Steve rocked my world when he reviewed an article from a back issue of Marathon and Beyond from 2001 with an article by Tom Osler, who wrote the book Ultramarathoning: The next challenge. In that article, Osler summarizes recommended training by saying that the average trained marathoner easily has the endurance to complete a 50 mile race, especially if they are willing to recognize their fatigue, run with "class", and walk from time to time.
Google quickly yields lots of resources on the topic, and suggests that the feat can be completed with 50-60 miles a week of smart training.
The Ultimate Running Experience
Runner's World Ultra Training Plan
*eyebrow raise* Fascinating...