What a great question? Culturally, Seattle is a real melting-pot, with a strong Native American history underlying more recent waves of Scandinavian and Asian immigrants. Seattle's uniqueness is based, in part, on the contributions of so many different cultures that have come together in Seattle. You can get a feel for the cultural richness of the greater-Seattle area by researching the variety of festivals, fairs, and events held in Seattle, and statewide as well. It's hard to know where to start, but a suggestion might be to look into all the small community celebrations which occur during the SeaFair summer celebration. There are dozens and dozens of important cultural events happening during the SeaFair celebration.
Thanks for an interesting question!