For bicycling on paved roadways, the marked bicycle route on Route 28 covers some pretty mountainous terrain, but the Seaway Trail between Alexandria Bay and Cape Vincent runs through generally flat or rolling farmland.
Uncle Sam Boat Tours offers tours that go through the Canadian side of the islands, but fall foliage is also worth catching. Sightseeing cruises take 2¼ hours, with options to stop at Boldt Castle or Singer Castle. The company also runs frequent 10-minute boat shuttles to the castles. Boats have heated, enclosed lower decks. Dinner and lunch cruises are available; reservations for meal cruises are required. Boldt Castle shuttles are $7, and dinner and other cruises cost up to $42.50. 47 James St., Alexandria Bay, NY, 13607. 315/482–2611. www.usboattours.com. Apr.–Oct.; call for schedule.