Unfortunately the Holland America/Princess pier is not close to downtown. Customs clearance was dead slow (almost 2 hours and we nearly missed our transfer). The exit area is poorly organized and none of the personnel seemed to have good information. Once downtown, downtown Seattle is walkable but a bit hilly, so you will not want to be dragging luggage. There is a convenient train line to the airport for just $2.50, so from downtown no transfer is needed.