Northwest Folklife is a four day event that takes place at the Seattle Center over Memorial Day weekend. The festival is free to attend and it's chock full of music and other performances. What you will find are a ton of musical acts at different stages around Seattle Center. Parking around the center will be tough, but there are lots of good transit options ranging from the monorail to bus service. The crowd will depend on the weather - the better the weather - the bigger the crowd.