Rainier Square Tower is a mixed-use skyscraper in the Metropolitan Tract of downtown Seattle, Washington. The 850-foot (260 m) tall, 58-story tower is located at Union Street between 4th and 5th Avenues adjacent to the existing Rainier Tower; it is the second-tallest building in Seattle. The $600 million project was completed in 2020, and is the tallest building constructed in the city since the construction of the Columbia Center in 1985.