Pike Place market is great, and go walking along the street where the piers are. Maybe see the aquarium. DO NOT bother with underground Seattle, It's ok, but not worth the hype and a good book will give you more info without creeping around under the city. See the stores and stuff near pioneer square though, its nice there. This is silly since you are going on a cruise but the r/t ferry boat to Winslow and back is nice and the view coming into Seattle is great. On a sunny day it is one of my favorite things to do. If you like gorgeous parks the arboretum is wonderful and there is a japanese garden and tea room that is a neat experience.