When visitors to San Diego want to experience as much of the city as possible in one day, they turn to the San Diego Grand Tour (which is actually three tours in one). Start the day off on the water with a cruise around the harbor before boarding a luxury motor coach to see downtown San Diego, Balboa Park, and the Gaslamp Quarter. Finally, it's off to Tijuana for an afternoon of shopping.
Tours can be booked online. San Diego Tours also offers many other packages, or you can choose to hop in one of their Go Car rentals and explore on your own.