The great divide mountain bike route runs 2,696 miles from Banff to the US/Mexico border. Before breaking the women's record by two days, including a stop in hospital, Lael Wilcox rode to the start from Anchorage.
I'm lucky enough to be visiting some parts of the route later this year (in a car), and in planning I've been looking at just what the route entails. Traversing the rockies and long stretches of desert, almost entirely off road.
In my stupid brain, it's not the distance or technicality of the riding that makes it feel impossible, it's the stress of dangerous wildlife and the logistics of getting to and from the start and finish.
Maybe I feel that way because it's so absurdly impossible that I don't even look for the conventional barriers.