What’s the easy way? Depends on where you’re coming from.
Folklife has put together a really great web page detailing all possible options: Driving and parking; public transportation; and biking.
Note that there’s a special Folklife shuttle operating Saturday, Sunday and Monday from Northgate and from Renton to Seattle Center. The fare is $2.50.
The page also has an interactive map to help you chart your course.
See you there!