The popular Seattle Underground Tour visits the eerie sunken storefronts of what was ground-level Pioneer Square before the Great Fire of 1889. Smith Tower, which overlooks the square, was the tallest building west of the Mississippi when it was completed in 1914. Ride the last manually-operated West Coast elevator up to the Smith Tower Observation Deck for a panoramic view of downtown Seattle, the waterfront and Mt. Rainier.
More info about Pioneer Square from Wikipedia.