I don't know if you like driving around but on nice day trip is to drive to Mukilteo and take the ferry over to Clinton on Whidbey Island. You can drive the length of the island and see some small towns along the way. One town is Coupeville. Small but interesting to look at. Lots of small shops and restautants. Penn Cove mussels are a local specialty. There is a museum/restaurant at the end of a pier that is interesting.
From Coupeville continue north to Oak Harbor the county seat of Island County. Oak Harbor's main claim to fame is the Navy Base. In general, Oak Harbor is clean and well laid-out. Continue on the main hiway to the Deception Pass Bridge. This is a beautiful sight! The bridge spans a narrow straight and there is a park that has trails that lead down to the water. Take a camera and shoot this bridge from every possible angle. The cliffs, trees, water and mist are incredible!
From there you can continue on to Anacortes and take a ferry to Victoria / Vancouver or to visit the other San Juan Islands. This area is beautiful even in the middle of winter. That is to say, the whole state.
Alternately, you can head back to Seattle on the side roads (this takes a while) or by I-5 (about an hour and a half) Stop by any city or town on the way. It is all interesting.
An interesting thing (for me) is when you get to the road that leads south from Anacortes, just before you leave Lopez Island, there is an Indian casino (the Swinomish tribe). Next door to the casino is a very well stocked tobacco shop. If you want to pick up any tobacco product (like a box of good cigars, hint, hint) you can get a pretty good price and avoid an UNGODLY state tobacco tax. I think the tax is currently at about 75%. There will be no more chances on the way to Seattle. There is another "rez" in Marysville, but last time I checked, they were out of the tobacco business.
My, how I DO go on about my hobbies! Sorry.
Just some ideas. Someone who lives there can tell you more about the area. You can also reverse the trip and it is just as interesting.
P.S. About the ferry. I lived on Whidbey for a short time (about 3 months) and commuted to a contstruction job daily on the mainland. The trip is short, about 15 or 20 min. But the things that can happen! Did you know that orcas (killer whales) have the right-of-way!? If a pod of whales crossed in front of the ferry, the ferry must stop. You could be in for a real treat as you watch them swim by. No guarantee but it is a possibility.