Must do's for a visit to Seattle include at least one trip down to
Pike's Place (a big, year-round farmer's market) and a journey out to
Mt. Rainier. In our three days in Seattle, we actually dropped by Pike's Place twice; the second time to re-stock on items we'd discovered the visit before. Seeing Mt. Rainier should be, at the very least, a FULL day. More if the weather's good, and you love the outdoors.
A couple of other highlights suggested by local friends were a ferry trip out to Bainbridge Island for brunch at the Skyliner Diner (Try the peach muffins! Don't bother trying to ask for the recipe.), and (if you're going up north) a drive up Chuckanut Drive towards Bellingham.
Quick Tips:
If you're in town the first weekend in August, try to catch the U.S. Navy Blue Angels at the Sea & Air show. They close the I-90 bridge to vehicular traffic, and people park along Coleman Park and walk out onto the bridge to see the show. It's a better view than going the actual site of the show itself.
Go to Mt. Rainier. On clear days you can see the peak from Seattle, but it's about a two hour drive to the park. Leave early in the morning. You'll want to take the scenic road around the east side, and you'll want to stop frequently to take pictures of the magnificent beauty of the region (at least on a nice day.) Also, bring plenty of water if you're planning on hiking. There are pleny of trails!
If the weather permits, which it didn't this trip, try a trip out to the San Juan islands. The previous July, the resident Orca pod was in the bay as we ferried over!!
Best Way To Get Around:
You have much more access to the natural wonders of the region if you have a car. With a car, you can also take a scenic drive out to West Seattle (to Alkai) to see the Seattle skyline.
Once you've reached wherever you're going, get out and stretch your legs. Seattle was designed for the active folk.