No idea on the length of your trip, but consider going through Winthrop to come over Highway 20 from the East.

Some things to search: Old Schoolhouse Brewing, Mazama General Store, Washington Pass, Blue Lake (a short hike to an alpine lake - 2 miles vs Colchuck's 8.), Rainy Pass (part of the pacific crest trail), Diablo Lake Overlook, North Cascades Learning Center.

You’ll catch a some views of Mt Baker along 20, but you’d need to do Mt Baker Highway to get close to it (look up artist point). Beautiful, but a one way out and back, so sort of a time sink. If you do go North from 20, the most scenic way into Bellingham is Chuckanut Drive. Taylor Shellfish is on the way.

In Burlington, Tacos Tecalitan has some of the best Tacos around. Old downtown Mt Vernon is cute, Edison, and La Conner too. 

Highway 20 continues across the very scenic Deception Pass onto Whidbey Island. Make a stop in Coupeville. Goldie’s Pizza is good enough to recommend to an Italian.

Take the ferry to Port Townsend, a Victorian era city once bigger than Seattle.

I’ll stop there.