Seattle is a huge sprawling metropolitan area with amazing amounts of natural scenic beauty nearby. Literally TONS of things to see and do within the city and in the great outdoors. Everything from beaches and ocean to mountains and snow sports. Maybe if you tell us a little more about yourself and traveling companions and interests we can better help with suggestions geared towards your preferences. Also, how much driving you are willing to do, and even if you'll have a car available.
Oops! I see you said May...my bad.