Watch the commuters come and go at Jamestown and Newport Ferry. Alternatively, book your own ferry ticket and admire the views from the water.
You'll be spoiled for sightseeing choice in Jamestown. Jamestown and Newport Ferry is a good place to begin here, but there are loads of other worthwhile sights to consider. Fort Adams State Park, The Breakers, and International Tennis Hall of Fame and Museum are near the ferry passenger terminal and will round out your day nicely.