The Tour de France has me looking at past rides in the Alps. I've done the Etape du Tour twice, and now I cannot fathom both how I was able to complete them, and how I could ever be in a position to even attempt a ride of that stature again.
100 miles, 20,000 feet of elevation, over 4 mountain passes, for close to 8 hours with 15,000 other people. Absolutely boggling numbers.