Tacoma is a great destination for a couple days with easy access to Gig Harbor. I’ve included things to do in Tacoma in the Olympia to Tacoma segment, but for this segment I’ll focus on getting to Seattle. While there are more direct routes, I prefer this one because it maximizes time on dedicated bike paths.
The first part of the segment is an ugly ride through Tacoma’s industrial port along Marine View drive and then a hill climb out of Commencement Bay on Norpoint way, but you are then rewarded with 5 miles of dedicated bike path on the BPA and West Campus trails.
That is followed by a traverse to into the Green River valley along 320th, 321st, and 316th streets. Another reason I recommend doing the route in the northward direction is to avoid the uphill climb out of Auburn, but it makes for a great coast into the valley.
A 5 mile bike lane from Auburn to Kent brings you to the Green River trail, a 20 mile trail you will use to complete your ride. The trail follows the infamous Green River to west Seattle where you can catch a ferry over to downtown Seattle. Your return to Portland is from the King Street Amtrak station in Seattle.
The river trail has several highway crossings so you’ll need to watch for signs or consult your phone’s map to make sure you don’t get off course. It’s really amazing, however, that the ride from Tacoma to Seattle can be completed primarily on a dedicated bike trail.