Avenue of the Giants marathon: Awesome run through the redwoods of Northern California. A shame that participation has dwindled. Guaranteed to be cool and shaded.
Any National Masters Championship road race. Since this is a bucket list, it would seem to have older runners in mind. And if you are pretty good in your age group it is fun to suddenly be competitive and not minutes behind the sub-5:00/mile pace guys. Plus, if you can afford it, it's fun to point for races in different parts of the country.