There are lots of possibilities if you do want to come this summer, as long as you accept that things will not be at their best. I would skip Seattle entirely——our city is definitely not back to normal yet, and while not dangerous it is also not particularly pleasant. But there are lots of nice places nearby you can head to after landing at SeaTac. You will definitely need a car! And do not worry about taking a rental car on the Washington State ferries; there are no such restrictions (as long as you are not heading into Canada, which is not possible now in any case). You DO need ferry reservations if you plan to visit the San Juan Islands, or to take the ferry between Port Townsend and Whidbey Island. All these places are nice to visit. Port Townsend is a personal favorite of mine and usually offers a continuous progression of music festivals—-blues, bluegrass, jazz—-but probably only “virtually” this summer. Look up “Centrum” at Fort Worden/Port Townsend if you are interested.
But what is your timing? The post above mentions wildflowers at Mt. Rainier in late June, but actually the Paradise flower fields are buried in snow until mid-July at least, and this year the snowpack is heavy and will last longer. I am hoping to see the flowers in August and we have reservations at Paradise Inn around the 10th. That may or may not hit the peak but it is always beautiful there.
The Paradise Inn is currently scheduled to open May 22 but if you go before mid-July you will be likely be joining the skiers and snowshoers up there. Still a place worth seeing. If you want to search for available rooms at whatever date, this is the website:
Some good options in Washington that haven’t been mentioned yet:
Most of the vineyards in our state are indeed in Eastern Washington, but there are lots of wineries just north of Seattle in the community of Woodinville. These offer tasting, and some have music (the San Michelle Winery usually has an outdoor summer concert series, but I don’t know about this year). There is a nice upscale hotel near there (I forget the name but can look for it).
There are also wineries with vineyards on Bainbridge Island (a ferry ride from Seattle, and on your way to Port Townsend and the Olympic Peninsula) and around Sequim on the Olympic Peninsula. Lavender farms there too.
A popular multi-day loop drive through the North Cascades and back:
Lots of nice lodging in Leavenworth on Highway 2 and in the Methow Valley on the North Cascades highway. Note that this road, which traverses North Cascades National Park, may not open until June.
If you take the Cascade Loop anti-clockwise (Highway 2 first), you return westward on Highway 20 which ends at Anacortes, the location of the ferry terminal for the San Juan Island ferries. Catch your (reserved) ferry and the islands (Orcas and San Juan are the most popular, and offer kayaking, hiking, nice B and B’s, and whale watching tours). Upon return to Anacortes, drive down across Deception Pass and then Whidbey Island. If you still have time and the inclination, take the ferry from Coupeville on Whidbey to Port Townsend and spend a few days there. You could visit Olympic National Park, but it is a lot of extra driving, and it is going to be extremely crowded this summer so lodging is becoming scarce already. So I would suggest saving that for another trip. Instead, from Port Townsend you can head south by various routes either to Seattle to end your trip, or into Oregon if that is your plan.
I will leave Oregon to others who know the state best.