What if Paul Revere had ridden a bike instead of a horse? That's sort of the idea behind Urban AdvenTours' historical tours of Boston, conducted by (sometimes) behatted guides who issue their proclamations from the seat of a bike instead of an exhaust-spewing duck. You can tour Fenway, the Charles River, downtown (Back Bay to North End), the Rose Kennedy Greenway, and other areas of Boston by bike with the green- and fitness-minded Urban AdvenTours.......