Leinster Gardens is a street in Bayswater, London. It has two false façades at numbers 23 & 24, constructed at the time of the original steam engine-hauled underground railway that had a short section exposed to the surface.
Locomotives were fitted with condensers to reduce fumes, but "venting off" was still needed in open-air sections to relieve the condensers and keep the tunnels free from smoke. In this upmarket area, the railway company hid this unsightly practice from residents. The false façade also maintained a continuous frontage along a prestigious terrace.
The façade is 5 feet (1.5 m) thick with 18 blackened windows. The doors have no letter boxes.
In the 1930s, a hoax was played on guests who were sold 10 Guinea tickets to a charity ball at Leinster Gardens, only to turn up in evening dress to discover the address was fake. http://en.wikipedia.org/wiki/Leinster_Gardens