Yes ... STP. Not the most entertaining route, but it is available in case you want to get from here to there or, more likely, from there to here. Remember that you can't get credit for a ride that counts elsewhere, so you can't ride the STP permanent at the same time you are doing the STP, but you can ride it back to Seattle (or to Seattle beforehand if you're from Portland).
The route is available as:
0918 Seattle to Portland
0918 Portland to Seattle
The Portland start is here: https://ridewithgps.com/routes/14760257
To get to the Amtrak station from the finish see this route: https://ridewithgps.com/routes/18933668
|Starts in:||Seattle, WA, US|
|Elevation:||+4978 / -4970 ft|