You can find London’s smallest police station tucked away in the southeast corner of Trafalgar Square.

But you can also be forgiven for missing it: It looks more like a neoclassical Tardis than a police station, and there won’t be a crowd of tourists gathered around it, merrily snapping away on their cameras.

Though the Lilliputian cop shop is not among London’s most popular visitor attractions, it’s certainly unique. It was built in the 1920s to serve as a watch-post and eye on Trafalgar Square, which has been a magnet for London’s protesters, rioters, and marchers (plus, for many years, pigeons). Inside, there’s only room for a single person.

In its heyday, the station was fully prepared for even the most passionate protests. It had a direct telephone line to Scotland Yard and castle-style slits in the walls to allow the single officer to keep an eye on any rioters. When the officer picked up the phone to call for backups, the light atop the tiny station would flash like a beacon, signaling to other nearby officers.

Sadly, if you peer through the windows these days, you won’t see a bored bobby—just lots and lots of mops. The station is now used as a storeroom for cleaners.