The Criterion Theatre

The Criterion Theatre is a subterranean wonder that exists entirely beneath street level. When it first opened in 1874, this design was so unusual that authorities worried audiences might be asphyxiated by the gas lamps used for lighting. To keep the theater operational, developers had to install a specialized air-pumping system to circulate fresh air, effectively making the Criterion one of the first air-conditioned buildings in all of London.