You know what's an easy day trip from SEA?.......ICELAND!!! That's right! I did it last winter! It leaves Seatac at like 2:45PM and gets into Iceland at 6:45am, then on the way back you get into Seatac at like 7pm. I did it in 2 days. I wouldn't go during summer as that's busy season, but definitely give it a try this winter. The paper tickets on Icelandair are kind of annoying though.