I have been to Seattles underground city and recall having somewhat of a spooky feeling but that could very well had been my imagination lol. Here is some info:
Seattle's first buildings were wooden. In 1889, a cabinetmaker 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. They never recovered from the subsequent drop in water pressure, and the Great Seattle Fire ended up destroying 33 city blocks.
While a destructive fire was not unusual for the time, the response of the city leaders was. Instead of rebuilding the city as it was before, they made two strategic decisions. First, they ordered that all rebuilding use stone or brick—insurance against a similar disaster in the future. They also decided to take advantage of the destruction 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 didn't back up during high tide in Elliott Bay.
To regrade, the streets were lined with concrete walls which formed narrow alleyways between the walls and the buildings on either side of the street, and 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", effectively raising the streets to the desired new level, generally twelve feet higher than before, though some places were nearly thirty feet.
At first, pedestrians climbed ladders to go between street level and the sidewalks in front of the 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 turned to amethyst-colored because of phosphorus in the glass), were installed, creating the area now called the Seattle Underground.
When they reconstructed their buildings, merchants and landlords knew that it would just be a matter of time before what was originally the ground floor would be underground, and what was originally the next floor up would be the new ground floor. As a result, there is very little decoration on the doors and windows of the original ground floor, but extensive decoration on the new ground floor.
Once the new sidewalks were complete, building owners moved their businesses to the new ground floor, although merchants carried on business in the lowest floors of buildings that survived the fire, and pedestrians continued to use the underground sidewalks lit by the glass cubes (still seen on some streets) embedded in the grade-level sidewalk above.
In 1907 the city condemned the Underground for fear of bubonic plague, two years before the 1909 World Fair in Seattle (Alaska-Yukon-Pacific Exposition). The basements were left to deteriorate or were used as storage. In some cases, they became illegal flophouses for the homeless, gambling halls, speakeasies, and opium dens.
Only a small portion of the Seattle Underground has been restored and made safe and accessible to the general public on guided tours.
Wikkipedia
