For sure, stay an extra day & ck out the science center. We went on the underground tour and based on the limited amount of time you're here, I'd skip it. Also, if your toddler might find it scary instead of cool...depends upon her personality...We only just went to it a few years back. The Argosy cruises do sound cool. I haven't been on one but both boys loved Tillicum Village and the view from out on the boat is breathtaking - I saw some photos a friend took.