Have you ever seen a manhole cover with little glass circles in it and wondered why it used to be different from the others? Were you aware that there have been if truth be told tunnels under the sidewalks and those manhole covers imbedded with glass circles allowed light into the tunnels below?
Underground hollow sidewalks and vaults had many uses when they were first installed in the late 1800s. Vaults allowed businesses to expand and utilize the unused spaces beneath sidewalks and alleys for storage and coal delivery. Hollow sidewalks allowed for delivery of merchandise, to allow people to shuttle from one place to some other without being seen (think prostitutes and speakeasy’s throughout Prohibition), and to allow construction of below ground shops. Hollow sidewalks were shared by all of the buildings on a block.
The writer spent 5 years researching these tunnels and she covers fourteen cities in Colorado that has them. The book features a listing of tours of the historic underground across the U.S.