One thing I think every Seattle kid should do is see the underground in Pioneer Square. In Seattle’s first neighborhood, there's a sidewalk UNDER the sidewalk. What's now the street-level entrance used to be a second-floor balcony.

You can only see the Seattle underground on a guided tour and it's worth the admission. Basically, all of downtown Seattle burned down in the Great Fire of 1889, an opportunity for a do-over. They blasted water at the hills, creating controlled landslides that filled in low-lying Pioneer Square. It's weird and nifty history you can see for yourself.