The Houston tunnel system is a network of subterranean, climate-controlled, pedestrian walkways that links 95 city blocks 6 metres (20 feet) below downtown Houston's streets. The system is approximately 11 kilometres (7 miles) long and is similar to tunnels in Dallas, Montreal and other cities around the world.
The first link in the Houston tunnel system was built in the 1930s by a business owner who wanted to connect two of the neighboring buildings he owned. Nowadays the entire system of tunnels are widely and heavily used by office workers and tourists. Only one building, Wells Fargo Plaza, offers direct access from the street to the Tunnel; other entry points are from street-level stairs, escalators, and elevators inside buildings that are connected to the tunnel. Access is allowed to the general public into these buildings with few restrictions, during normal operating hours, in order to reach the Tunnel where all kinds of shops and businesses can be accessed.
The City of Houston's website said it this way, The downtown Tunnel System is an interconnected series of restaurants, shops, etc. servicing all those who wish to avoid the characteristic Houston weather, while walking around in air conditioned comfort over the course of several miles.
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