Underground Tour, Seattle
I grew up here and never did the Seattle Underground Tour. It is the kind of thing you only do when tourists are in town. When I returned as a tourist, of course I had to do the tour. It's worth it - you'll learn some history of Seattle, and it is pretty interesting to learn how the original city sunk and then the present city was built on top of it. The tour guides are amusing - most likely stand up comedians by night. Definitely not your average docents.
The Underground tour gives you a cool peek at what Seattle was like before The Great Fire razed 13 blocks of downtown in 1899! Everyone in your family will enjoy the 90 minute tour beneath Seattle's busy modern streets, given by interesting guides who are fun and knowledgable.
Although few people seem to know about it, I would say that the single must-see activity in Seattle, especially for those interested in history, is the Seattle Underground Tour. Although full of cheesy, lame jokes, it provides a fascinating and little-known insight into Seattle's colourful, very sordid, and really quite strange past. The emphasis is on the city's beginnings as a seedy logging town, its early chaotic growth before the 1889 fire that pretty much wiped out the city, and how the downtown was originally rebuilt afterwards. The story is interesting, and the underground sites are great to see.