The Seattle Underground refers to a network of underground passageways and basements in downtown Seattle, Washington. These tunnels were created in the 1890s after the city raised its streets to prevent flooding. The original street level became obsolete, leading to the construction of a new street level above the old buildings. Today, the Seattle Underground is a popular tourist attraction, offering guided tours that explore the history and architecture of the area. Visitors can learn about the city's early days, including the challenges it faced and the unique solutions that were implemented to create a thriving urban environment.