If you're looking at Amtrak trains as an option to get to the Seattle airport, or you just want to take a rail journey, here are some discount codes to consider:
The biggest percentage savings in the nation is probably on the Cascades trains through Oregon and Washington, up to Vancouver, BC. The transit-friendly city of Portland, OR sponsors code H750, which lets you buy one ticket and get one free if two people are riding together anywhere on that line through May 23 -- and yes, that includes trains (but not buses) to Canada.
Lonely travelers to the Northwest need not fear: Seattle has you covered. Use code V777 for a 25% discount on any Cascades train if you're traveling alone, through May 16th.
AAA members can also get 50% off a second ticket, or 25% off business class and sleeper seats on most trains except California and Northeast Corridor trains. Use code V644 and be prepared to produce your AAA membership card on demand. That code is for booking through Feb. 28 and travel through March 15.