Seattle Underground

The Seattle Underground is a network of underground passageways and basements in downtown Seattle, Washington, United States that was ground level at the city's origin in the mid-19th century. After the streets were elevated these spaces fell into disuse, but have become a tourist attraction in recent decades.

Seattle's first buildings were wooden. On June 6, 1889 at 2:39 in the afternoon, a cabinetmaker (Jonathan Edward Back), accidentally overturned and ignited a glue pot. An attempt to extinguish it with water spread the burning grease-based glue. The fire chief was out of town, and although the volunteer fire department responded they made the mistake of trying to use too many hoses at once. With the subsequent drop in water pressure none of the hoses were effective and the Great Seattle Fire destroyed 31 blocks.

While a destructive fire was not unusual for the time, instead of rebuilding the city as it was before, the response of the city leaders was to make two strategic decisions: first, that all new buildings must be of stone or brick, as insurance against a similar disaster in the future; and second to regrade the streets one to two stories higher than the original street grade. Pioneer Square had originally been built mostly on filled-in tidelands and, as a consequence, it often flooded. The new street level also assisted in ensuring that gravity-assisted flush toilets that funneled into Elliott Bay did not back up at high tide.

For the regrade, the streets were lined with concrete walls that formed narrow alleyways between the walls and the buildings on both sides of the street, with a wide "alley" where the street was. The naturally steep hillsides were used, and through a series of sluices material was washed into the wide "alleys", raising the streets to the desired new level, generally 12 feet (3.7 m) higher than before, in some places nearly 30 feet (9.1 m).

At first pedestrians climbed ladders to go between street level and the sidewalks in front of the building entrances. Brick archways were constructed next to the road surface, above the submerged sidewalks. Skylights with small panes of clear glass (which later became amethyst-colored because of manganese in the glass) were installed, creating the area now called the Seattle Underground.

...
Wikipedia