Lewis and Clark built a trail that brought them from St. Louis (St. Charles area) clear across the country through Missouri, up through the Dakotas, across Montana, and up through Washington state. Together Lewis and Clark traversed their way across the country, and a large portion of their trail is still available for hiking patrons to explore right outside of St. Louis.
A few weeks ago, I was fortunate enough to go out to the Lewis and Clark trail and hike around for the afternoon. I would highly recommend the experience. You can find more details out here.