The idea that immediately springs to my mind -- one that I'd love to do in somewhat less ambitious fashion (like for a couple of weeks each year) would be to retrace some classic journey, doing portraits of the people who live on that path. Route 66, or the route taken by the two main characters in Zen and the Art of Mororcycle Maintenance might be good. Maybe a better idea would be to stock up on contingency food, water & hygene materials and eschew any kind of map or GPS and just go where the wind or the need for gas takes you.