It's probably one of the harder bike races out there. 100% self support, all dirt, no rest days, no team sag, none of that. People get sick, injured, sick of racing; weather can be terrible. I think a guy died of hypothermia one year. It's really hard on the bikes. A rabbit at holes in his shoes. They don't carry stoves as cooking takes too much time. You get a hamburger in a town and put three more in your bag to last you to the next town.
Here's an interesting link.