Argosy offers great tours of Seattle by boat. Be sure to take the Harbor Locks cruise. It's worth the $15 upcharge to the City Pass coupon. You'll see seaplanes take off and land on Lake Union, and get great views of the famous floating homes. You'll pass through the locks into Puget Sound, and get amazing views of the city and Mt. Rainier. The staff is friendly and knowledgeable. Definitely one of the best parts of our trip.