The Grand Central Terminal is one of New York's iconic landmarks, and as such, it's one of the most visited attractions in the city. Being a revolutionary and historical landmark, the Grand Central sure holds a couple of secrets, ones that are not supposed to be easily given out to the public.

And for this very reason that the MTA's oldest tour guide was suspended indefinitely. Dan Brucker, who have worked as a Grand Central docent-in-chief for three decades, was suspended because of his "off-limits tours" behind the backs of the MTA.

According to the New York Post, Dan Brucker was the one responsible for giving behind-the-scenes tours of The Grand Central, in which areas include a control room, the inside of the Tiffany clock atop the building facing 42nd Street, secret rails that carried former President Franklin Delano Roosevelt's limo underneath The Waldorf-Astoria hotel, and many more.

Although the MTA is informed about these tours, they found out that Dan Brucker hosts such tours even on his days off, which means a very serious security risk to the MTA. A source told the Post said: "There's a reason why these places are off limits - for security. You don't want people knowing about certain stairways and where they lead to. What if he's unknowingly taking a member of ISIS?"

Concerned officials said they are still currently investigating the matter. Brucker, even though he was employed by Orpheo, a tour company, was paid by the state itself, according to Gothamist. When sent an email regarding the incident, Brucker's MTA email address simply read: "Dan Brucker no longer works for Metro-North."

No other tour Grand Central tour guide gives this insider tours other than Brucker. Because of his suspension, no behind-the-scenes tours are available anymore.

Brucker's knowledge about the secret areas inside the terminal is extensive, and it is perfect for those curious about the history of the Grand Central. However, security risks still outweigh tourist curiosity, making it a serious offense. Dan Brucker is not available for comment.