Leinster Gardens in Bayswater is certainly one of the stranger things to be found in London. The houses at numbers 23 and 24 are fake houses, built at the time of a steam powered underground railway in the 1860's.
The houses were built without windows and instead allowed the steam from the tube to be vented into the air from the tube network.
UG: Bayswater 0.28km
UG: Queensway 0.35km
UG: Lancaster Gate 0.58km
Always check details regarding opening hours, accessibility and pricing before travelling.