There is good old Pike Place Market (visit the first Starbucks, although the line up can be long), take a pic at Kerry Park, visit Sky View Observatory at Columbia Center to get 360 degree view of the city or Space Needle, or Outlet shopping at premium outlet in Tulalip.
But I am sure you can find more here as per Tripadvisor:
http://www.tripadvisor.ca/Attraction...ashington.html
If you are renting a car, the rush hour traffic can be real bad so I'd avoid it as much as possible.