For us seniors (we are 82 and 84 years old, respectively): the boat ride. It is a spectacular experience.
The tour in its entirety was full of unforgetable enjoyments, due largely to our amazing driver and tour guide, Debbie, who filled us with interesting facts with a winning smile, led the group at all the important times, and flitted from one to another of us at every stop, making sure we did not miss a thing.