Dark secret behind completely windowless 29-storey skyscraper in New York

What's more scary than an ominous skyscraper... an ominous skyscraper without windows.

This terrifying building in New York gives off very eerie vibes as locals still don't know what goes on inside.

Could it be a secret alien hideout? Or perhaps where the powers that be get up to no good?

Well, Tom Hanks was, in fact, the first to make the observation after sharing a photo of 33 Thomas Street back in 2017.

"This is the scariest building I've ever seen! WTF goes on inside?" he tweeted alongside the image.

TikToker Eric Guidry (@e.guidry) has thankfully come to the rescue and explained what the building is actually used for.

"So that building in New York, this windowless building in San Francisco, this one in Chicago, this one in Austin and hundreds more buildings placed conspicuously across the country, in very populous locations,” Guidry says in the clip.

It turns out that the buildings are all part of AT&T's long lines network.

"Before we had digital telephony, the lines on your phones physically connected to the person on the other end's phone.

"That meant we need these massive switching hubs. Most of those buildings I showed were built in the '70s [or earlier].

"That means they didn't require actual operators.

"And because this machinery didn't particularly care if there was light or not, they just decided, why add windows?"

Giving more information on the specific AT&T building in New York featured in the original TikTok video, Eric said: "That building is 33 Thomas Street, which is known to be one of the most secure towers in the world.

"It has enough gas, water and electricity to be able to continue running independently for up to two weeks and is supposed to be able to actually withstand a nuclear blast... within reason.

This is the scariest building I've ever seen! WTF goes on inside?? Hanx. pic.twitter.com/nXeUI64rXm

— Tom Hanks (@tomhanks) June 2, 2017

"Although most of the equipment has been digitalised and you don't need it for phones, it's still critical for network and internet infrastructure.

"In fact, if you're watching this in the US, this video probably went through one of those buildings."

However, several conspiracy theorists believe that the building has been used as a National Security Agency (NAS) surveillance site.

And in 2016, non-profit organisation, The Intercept, claimed that there was 'compelling evidence', including leaked documents from NSA whistleblower Edward Snowden, that pointed towards the building having been used as a surveillance site, code-named TITANPOINTE.

According to their 2016 investigation, a former AT&T engineer said there is 'a major gateway switch' that 'routes all calls between the US and other countries around the world'.

While other theories are a bit more crazy - ranging from vampires to 'lizard headquarters'.

So who knows?