In the mid-19th century, London pioneered urban underground transportation with the Metropolitan Railway, the precursor to today's London Underground. Built using the 'cut-and-cover' construction method, the line required digging deep trenches along street routes and roofing them over. However, early steam locomotives created a critical environmental challenge: condensed steam, soot, and carbon monoxide rapidly filled tunnels, threatening passengers with suffocation.
To alleviate this, engineers designated open-air sections along the route where locomotives could vent smoke and steam into the atmosphere. One such venting pit was positioned directly along Leinster Gardens in upscale Bayswater. The local wealthy residents were horrified by the prospect of an unsightly gap in their pristine terrace of grand mid-Victorian houses.
To preserve the aesthetic uniformity and high property values of the neighborhood, the Metropolitan Railway Company constructed 23 and 24 Leinster Gardens in 1868. These structures are complete illusion—a five-foot-thick brick facade designed to match the Greek Revival architecture of the adjoining properties. The dummy houses feature heavy neoclassic porticos, ornate window dressings, balustrades, and dark-painted windows to give the illusion of inhabited rooms.
Behind the brickwork lies an open pit exposing subterranean tracks where district and circle line trains pass through. The doors have no letterboxes or handles, and the back is supported by massive steel beams. Over the decades, these dummy houses became local lore, famously featured in Arthur Conan Doyle's Sherlock Holmes universe and serving as the target for famous practical jokes, including a 1930 prank where fake charity ball tickets were sold directing unsuspecting guests to the hollow doorway of number 23.