I just noticed how close Seattle is to Portland, OR, and thought, hey, I might as well stop there while I'm at it. What would be the best way to get to Portland from Seattle?
Take Amtrak down there. It's probably the easiest, most relaxing and cost-effective way down there, plus, you get to see a ton of nice scenery along the way. You would go to the King Street Station in Seattle and ride to the Union Street Station in Portland. The ride is 3 hours and 40 minutes and costs $33 per adult. Once in Portland, public transportation is fantastic. There are buses and streetcars everywhere that run very frequently and if you have a smartphone, the schedule on the Google Maps app is very accurate.
Another option is to drive. It's about a 3 hour drive if you wanted to rent a car. Parking in Seattle is horrible, but fairly easy in most parts of Portland. Just drive carefully and watch out for the highway patrol up there. They seem to be everywhere!
Train is definitely the best way. It takes approx. 3.5 hours. Beware, though, Amtrak trains can be late because the freight trains have right-of-way here, as opposed to east coast where commuters have it best.
Take your laptop or tablet, and enjoy watching all the people with bikes at the train station!
Stay awake for the portion of the ride from Olympia through the
Puget Sound. It is beautiful, and you get to see the
Tacoma Narrows Bridge. Look up "Galloping Gertie" for video of the original bridge in a storm!