In the midst of galloping growth at the turn of the twentieth century, Seattle's city leaders seized on the confluence of a roaring economy with the City Beautiful movement to hire the Olmsted Brothers landscape architecture firm to design a park and parkway system. Their 1903 plan led to a supplemental plan, a playground plan, numerous park and boulevard designs, changes to park system management, and a ripple effect, as the Olmsted Brothers were hired to design public and private landscapes throughout the region. The park system shaped Seattle's character and continues to play a key role in the city's livability today.
I don't know enough about Seattle parks for this to really resonate with me (not much is jumping out as "I know that place! I know what they're talking about"), but the history and Olmstedian principles are interesting.