Washington is a pretty state of two extremes. The Rocky Mountains block most moisture from traveling East, so the Western part of the state is very wet, and the Eastern part is very dry. Seeing as I live in Southeastern Arizona, I prefer to visit the wetter parts of the state.
The sad thing about Washington is that the entire West Coast depends on the I5, and it’s bad, really bad. Not only is this interstate under-maintained, it’s also trying to accommodate more traffic than what it’s capable of handling. Therefore, expect lots of delays, especially when you hit the metropolitan areas, like Tacoma and Seattle.
Be sure to visit Mt. St. Helens National Volcanic Monument and Mt. Ranier National Park. The latter has incredible grand vistas and wonderful wildflower blooms, with nice paved trails at Sunrise Visitor Center.
Another must-see is Olympic National Park, which has one of the wettest Rain Forests in the continental US, Hoh Rain Forest. The park has many hiking trails, suitable for all types of hiking and backpacking.
The entire Olympic Peninsula is a great place to visit, but be aware that it’s isolated, especially on the West coast – Ruby Beach and Beach 4 are a long way from anywhere.
The small towns along the Eastern and Northern part of the Peninsula have some wonderful old architecture with lots of photographic opportunities. One of my favorites is Port Townsend.
And bring rain gear. You’ll need it, regardless of the time of year, especially on the Peninsula.