The Harborside Fountain Park (bottom center and left center) is filled with giant, spouting fountains and very fun to walk around and explore. Lots of kids there were in full swim mode a very refreshingly wet.
Along the boardwalk we happened upon a Sunday Farmer's market. E protested (aka a bit of a tantrum) about how boring it was and how he hated markets - this is just at first glance. After moping through he cheered a bit with a balloon sword.
There is lots of Aquatic and Navy art to check out and I'd still be there taking pictures if I tried to capture it all.
We enjoyed watching the ships of all kinds, including giant Navy Destroyers, Aircraft Carriers, ferries and Aircraft Carriers. There is a historic Naval Destroyer called the U.S.S. Turner Joy that has been turned into a museum, but we didn't have time for that (note there is an entrance fee).
Our favourite thing was the (free) Puget Sound Navy Museum in fact we literally had to run out the door and down the dock to catch our ferry and so didn't see everything...
There is an entire children's room with activities including dress-up.
The boys loved all the hands-on activities and interesting information. The interactive touch screen about an aircraft carrier was a highlight, as well as cool artifacts, and set ups of current living settings on a boat.
A great stumble for a Sunday afternoon worth of activities. Worth a day-trip from Seattle (plus the ferry ride is fun by itself!)