Giant Network Of Tunnels Fills Chicago’s Underground, History Books

In total, 60 miles of tunnels were built starting in 1899 by the Illinois Telephone and Telegraph Company, which later became the Chicago Tunnel Company. The tunnel company created “tunnel air,” which was pumped into city buildings like air conditioning, according to atlasobscura.com. The website noted the clay soil removed by hand that made the tunnels was used to build up “low lying areas on the waterfront.”