Man who worked in mysterious 29 story windowless skyscraper in New York City describes what it’s like inside

There are many large buildings in New York City but none are more larger - or more mysterious - than the skyscraper located on 33 Thomas Street.

In a forest of glistening plate glass, the 29-story building certainly stands out as it pays homage to a unique style of architecture.

Oh, and there's no windows either.

And it's because of this reason that many have wondered what actually goes on inside there, because how would you know without being able to see inside.

Well, one man who claims to have worked there has revealed what he saw when he went inside.

Mystery surrounds the building (Roy Rochlin/Getty Images)

Speaking to The Daily Mail last year under the condition on anonymity, the man says that he was invited, along with his son, in the early 2000s to work as a steamfitter - which involves someone installing wiring and pipes within a building.

According to the son, they were forbidden from entering into certain rooms.

He said: "There were rooms we couldn't get into. They specifically told us not to enter, and we couldn't ask what's inside or why we can't go in."

He claimed that him, his father and the rest of the team were ultimately forced to install wires around the room.

He further claimed that crew supposedly came across confidential papers in a cabinet in the basement - and what makes it even more interesting is the documents supposedly detailed what to do in the event of a radiation attack.

If you were to look into it further, you'll find the official use of the building is as a telephone interchange, and it was formerly known as the AT&T Long Lines Building - so basically just a place to wire up tons of phone lines.

The man has revealed what it's like inside (Roy Rochlin/Getty Images)

According to a TikToker, the building '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'.

However, despite this knowledge, people have come up with their own wild predictions as to the building's use.

One theory has suggested that the building is some sort of nuclear shelter - which seems a pretty wild conclusion even for conspiracy theorists.

While another theory is that it's a supposed listening post for the National Security Agency (NSA), called 'Titanpointe' - with an investigation by The Intercept claiming that parts of the building were dedicated to surveillance.

However, until anyone tells us otherwise, the simplest explanation is probably the correct one in that the building is, in fact, used for telephone interchange.

UNILAD has contacted AT&T for comment.