An air-conditioned system of tunnels underneath downtown Houston connects 95 city blocks and over 20 commercial buildings. The tunnels are full of dining options and various shopping/service locations catered towards the employees of all the offices occupying the buildings above.

The tunnel system has been around for nearly a century. The earliest known tunnels date back to the 1930s. According to the Houston Chronicle, one of the first tunnels connected two buildings owned by former Texas Governor Ross Sterling: the Houston Post-Dispatch and the Sterling Building. The tunnel ran beneath Fannin Street. Around the same time, entertainment entrepreneur Will Horwitz had a tunnel connecting his three theaters, the Travis, the Texan, and the Uptown.

According to architectural historian Stephen Fox, the idea of a system of shared tunnels came about in 1956, when the Bank of the Southwest was linked to the 1010 Garage and the Mellie Esperson Building. As the city grew in the 60s and 70s, so did the underground tunnels.

Each section of the tunnels has its own aesthetic, often an extension of the buildings directly above, which vary wildly from haphazard and dingy to spacious and modern. The tunnels are only open during the weekday business hours.