22-23-Leinster-gardens-facades-contrast by Wikimedia Commons
In 1863, the world's first underground railroad was created, in which long stretches of tunnel were dug and the covered over on the surface to hide the railway. The Metropolitan railway, as it was named, carved its way from Paddington to Bayswater in 1868. In order to continue the railway line, two five storey houses had to be demolished from the row of houses of which they were a part.
The railway was continued, and the surface where the two narrow houses had stood was left open to vent smoke from the train as it passed under the spot. Open areas were used regularly along the stretch of track to vent smoke out of the tunnel, but it was unsightly sitting in a row of houses. To remedy this, two facades were built, creating the illusion of houses existing at numbers 23 and 24, Leinster Gardens. A 5-foot-thick slab of wall was constructed with painted windows, fake doors, and even terraces to match the neighboring houses. But if one heads around back, the game is up, revealing the track and the fake houses concealing it from view.