- Seattle Center (EMP, Sci-Fi museum, Space Needle) are decent.
- Pike Place if you want to do shopping.
- The Mariners are terrible this year, but visiting Safeco Field is an experience in and of itself.
- Boeing tour is up in Everett.
- St. Helens is about 150 miles away. Rainier is closer, and if you plan on driving, is a more scenic drive if you follow the SR-410 route.
- Satruday or Sunday brunch at Salty's in West Seattle is an absolute must.
- I would highly recommend Hurricane Ridge out in the Olympics. It's out by Port Angeles, and is a day trip, but the scenery is awesome.
And if you're really into hiking/climbing, try your luck by climbing Mt. Si or Mailbox Peak.