Seattle Aquarium
What more appropriate city than Seattle, which is themed on its waterways and is surrounded by various bodies of water on three sides, for an aquarium. It features exhibits not only on the usual Northwest suspects such as reefs, marine mammals, salmon, various Puget Sound fish, and the like, but also mountains, birds, and even Antarctica. Situated on the waterfront.
Cinerama
The best theater in town and another Seattle landmark, it's known for its "cinerama" screen, which basically means it's larger than the competition's and slightly curved, designed for the 70mm films popular in the 50's and 60's. Refurbished to modern standards in the 1990's by Microsoft co-founder Paul Allen, it's in peak form today and is the place to see an event film like the latest :Star Wars" spectacular.
Museum Of Flight
Found near Boeing Field in south Seattle (a handful of miles from downtown), if you're an aviation history buff you'll do no better than this sprawling facility. See Air Force One, the Concorde, run a flight simulator, comprehend the breakthrough of the Wright Brothers, and see scores of planes of every variety. Just what you'd expect so near to the home of Boeing.
Pacific Science Center
This sprawling science museum includes everything you've come to expect and a little bit more. See laser shows, IMAX movies, high-tech exhibits, a dinosaur exhibit, outdoor exhibits, a butterfly exhibit, and various special-event exhibits depending on the time of year. Armies of kids will be underfoot everywhere, so time your visits appropriately (which means not when classes are in session).
Seattle Children's Museum
When you're anxious to occupy the kids' time for most (if not all) of a day, you'd be hard-pressed to do better than a museum that's just for them. They can learn about Northwest forests, "sail" to foreign lands, play fireman, explore their artistic sides, see how well they can act in a faux theater, and many other things sure to delight them (and the kid-at-heart in you).
Center High School
The heart of the northern section of downtown, this is a sprawling nearly ninety-acre site which contains numerous Seattle attractions, including Seattle Center Monorail, Fun Forest Amusement Park, Key Arena (SuperSonics), Children's Museum, performing arts (ballet, opera, etc), Experience Music Project, Science Fiction Museum, Pacific Science Center, an international food court, and more. Bring your walking shoes.
City of Seattle Parks & Recreation Department
As centrally located as zoos come, this one offers more than the usual animal exhibits. You can go on an African savanna safari, ride a pony, explore a barn, among many other things that will consume most of a day. All the animals you've come to expect are there too, of course, so it's typical in that respect. Children are admitted for $7, adults $10, and toddlers up to age 2 are free.
Mt Hood Railroad & Dinner
Fewer than sixty miles east of Portland, this classic railroad's four-hour round trip is one of the best ways to see the Mt. Hood area. Built about 100 years ago, this vintage engine will take you from the Columbia Gorge to the foothills of Mt Hood, April through December. One package even offers a narrated tour, while others will provide you with dinner.
The Elliott Bay Book Company
Situated in an historic building dating back to 1890, in the midst of a revitalized Pioneer Square, Elliott Bay Book Company is the area's most renowned independent book seller. Famous for the attractive cedar shelving along brick walls in many different rooms, the store contains over 150,000 different titles. New, used, and antique.
Blackfish Gallery
Blackfish is a cooperative gallery, one of the oldest on the West Coast. A few dozen local artists own and manage the gallery, which also presents theme shows which variously features local artists such as the works of art students. The portfolios are impressive and worth checking out if in the area.