1. 23 & 24 Leinster Gardens, London
The first steam engine underground railroads required open-air vents so that the tunnels didn’t get too clogged with air. But when there needed to be a vent in the middle of an upscale neighborhood, the railroad decided to camouflage it with the facade of a gorgeous townhouse. One thing’s for sure, this fake building is sitting on some mighty valuable real estate!