The Rainier Tower in Downtown Seattle was completed in 1977. While it does fall a few years outside of the Mid Century Modern era, the clean lines and design of the building makes it a good example of Mid Century Architecture.
The Rainier Tower was designed by Minoru Yamasaki who also designed the World Trade Center in New York City and IBM Building in Seattle which sits across then street from the Rainier Tower.
The building has a unique appearance because it sits atop an 11 story base that tapers inward toward the ground, giving the building the appearance of defying gravity! The building is 41 stories tall and is located at 1301 Fifth Avenue in Downtown Seattle.