Completely agree on the Million Dollar highway. I've done that many times in F350's/F450's towing 30k trailers, and also once in a snowstorm. South to North isn't bad as you're always next to the mountainside in the sketchy parts, but North to South definitely has the pucker factor! There are a bunch of others with similar dropoffs in Colorado too, like Loveland pass, Hoosier pass, etc.

Would love to eventually ride it on a motorcycle but haven't made the time to make it happen.