I was browsing Reddit a few nights ago and hadn't bothered logging in, so I was subjecting myself to the default subreddits. One of them, MildlyInteresting, lived up to its name.
Someone posted a picture of this house, which looks like it's nothing but a facade. After some discussion, including natives saying, "what do you mean 'lost'? [Museum I've never heard of] is just two blocks away," and some people thinking it's a false front for a Tube ventilation or electrical station, the truth came out.
The building is called The Thin House. Since London's general attitude toward a street-grid system is, "screw that," the Underground tracks going into the South Kensington station are at an odd angle to the street. The house is something like 5 feet thick on one side, and I'm guessing 25 or so on the other -- it's wedge shaped. It's in a part of the city called Thurloe Square, which given that I spent roughly 48 hours in London I had no idea where this was. London's a pretty big place, odds are I was nowhere near it.
(As an aside, it has an apartment that's currently for sale. 489 square feet, probably about the size of my last apartment in Pittsburgh, and it's yours for just $1,050,000.)
Since I was staring at Google Maps anyway I decided to zoom out. First thing I recognized was the A4, Cromwell Road. The hotel I stayed at was just off of Cromwell. But that's got to be a main road through a good chunk of the city so that doesn't mean anything.
Zoom some more, and pan a bit... and there's the Museum of Natural History. Between walking to find a Thai restaurant nearby and the tour bus driving past it, I saw almost as much of that museum as I did the hotel. It turns out the house was just a few minutes' walk from the restaurant.
I wish I'd known about it while I was there, I would have stopped by and... pretty much taken the exact same pic the guy on Reddit did. But at least it would have been mine.
Edit, 8:50 AM: Speling. Of course I never saw it over a handful of proofreads.