The Pinellas Trail is a 34 mile hiking/cycling track that runs between St Petersburg and Tarpon Springs. Free guides to the trail are available at any of the Chamber of Commerce visitor centres between the two destinations. The guides are great, picking out places of interest and giving easy to use maps and mileage charts. There are loads of places to stop/start, allow time to detour and explore a bit more. The trail is well marked. If you don’t want to do all 34 miles why not take the bus to your selected start point. Many buses have special bike carriers at the front so it couldn’t be easier.
A couple of points specifically about cycling in Florida: you MUST wear a helmet if you are under 16 even if you are just a passenger, every cycle must have a brake or brakes that allow you to stop within 25 feet from a speed of 10 mph on dry, level, clean pavement. A cycle used between sunset and sunrise must have lights. You can’t carry passengers unless your bike is equipped for multiple riders!!