What a great bonus to have a paved bike trail along the intracoastal waterway. We rented bikes right off the trail (at a bike shop in the plaza off Rte. 41 with Big Lots), and rode to our heart's content. You can make stops along the way, off the trail, and spend as little or as much time as you like.
Here's a link to a PDF of a trail map: http://www.venicegov.com/Files/Parks/BikeTrailMap.pdf