Not a tour but an option:
The historic Rhodos town is right next to the cruis port. There you need to walk anyway, thus you could see as many or as few of the sights, alleys, churches, palaces and museums as you like on your own.
Once you have passed through the ancient part you get to a large square where you also find most busstops. There is a direct bus to Kallithea Springs, running every 30 minutes.