There's a mysterious 29 story windowless skyscraper in New York City and no one knows what it's used for

New York City is home to a multitude of mysteries, as any city of such size would be, after all who knows what you could hide in plain sight?

Among the many strange things in New York is a skyscraper located on 33 Thomas Street. I know you're thinking, skyscraper in New York, big deal, but just wait until you take a look at this building.

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33 Thomas Street cuts a very striking silhouette across the city. In a forest of glistening plate glass, this building is an homage to the brutalist style of architecture, and even if you're not a fan of brutalism you have to admit it looks pretty stunning.

But the one thing which has people talking about it is the complete absence of windows from the flanks of the building. Instead, it rises into the sky like an obelisk of concrete.

The lack of windows has led many people to question what on earth goes on inside. It looks like something out of Terry Gilliam's dystopia Brazil, or Orwell's description of the Ministry of Love in 1984.

It certainly begs questions about what the interior of the building must be like without any windows in there, like another world entirely separate from the city outside.

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The official use of the building is as a telephone interchange, which would make sense given that you don't need windows to be able to wire up phone lines.

However, some investigations have linked the building to a National Security Agency listening operation, claiming that it may also be home to mass surveillance equipment.

Given the building's imposing appearance, it's not difficult to see why it has captured people's imaginations. The plain concrete surface, enormous jutting blocks and simple shapes are almost reminiscent of some great ancient monument.

People have come up with some pretty wild speculations as to what goes on in there. Among them is the rather odd theory that the building is some sort of nuclear shelter - which seems a little outlandish.

I'm no architect, but my impression is that a tall thin building would be the last structure you'd want to use to withstand a nuclear blast. Anyone who has played Jenga will know why that would be a terrible idea.

But as much as I hate to burst the bubble, the simplest explanation is probably the correct one, meaning that it is an enormous telephone interchange.

As to whether or not it's the site of an NSA surveillance post, an investigation by The Intercept tied it to a nearby FBI building.

Maybe it is, or maybe it's a conspiracy.