Note that although Bellair Airporter makes a trip north from the Seattle-Tacoma airport about every two hours, it only makes one trip a day from the downtown Seattle Sheraton Hotel, 1400 6th Ave. http://www.airporter.com/dev_doc/board.htm
. The King Street (Amtrak) Station is located at 303 South Jackson Street, about a mile away. But, if you have to stay overnight to make connections, you can check out Pioneer Square, the Klondike National Historic Park, the Seattle Visitor Center, Safeco Field (Seattle Mariners) and the waterfront.
In Anacortes the Airporter stops at Old Salts Deli-
Skyline Marina, the Washington State Ferry Terminal, and the Shell Station at 14th & Commercial. There are several motels along Commercial and nearby. You can dip your wheel in nearby Padilla Bay (best looking at high tide), or ride around to Washington Park which is off Rosario Strait. (Both are salt water, but neither is the ocean itself.)
Have a great trip!