There are secrets embedded in every nook and cranny of the city, from the tokens paved into the streets to clandestine "man caves" buried underneath Grand Central Terminal. But few places have captured the imagination of in-the-know New Yorkers like 58 Joralemon Street in Brooklyn Heights. What appears on the outside to be a pretty typical residential townhouse is actually an MTA vent and unmarked emergency subway exit with a rich backstory.

Read More: Learn about the history of 58 Joralemon Street

The townhouse has been the subject of much theorizing over the years, yet almost no one has been able to get a look inside to see the "mystery underground portals," as one website put it back in 2014. While only select transit employees are allowed to enter, it hasn't stopped people from speculating on what is happening with those mystery underground portals. One such person is Ben Tupper, who recently created 58 Joralemon: The Game, set at the mysterious address—and it's probably the most niche online game about obscure NYC minutiae since MTA Country featuring Gregg T.

Tupper, 34, and his wife have lived in Brooklyn Heights for about five years now, and he calls 58 Joralemon one of the highlights of their neighborhood.

"For our wedding, [my wife] took a crew of our friends and family around Brooklyn Heights on a little tour, and pointed out all the interesting things in the neighborhood, including that subway vent," he said. "I actually went out today and walked by it, and I saw two British tourists looking at a map. I pointed it out to them, and I said, 'See that house? That's not a house.'"

Tupper, currently studying math at City College, decided to practice coding by creating a Myst-style graphic-adventure puzzle game during his winter break. He started to wonder where he could set such a game.

"I figured it was much easier to draw orthogonal lines than to try to draw some organic landscapes," he said. "So I started trying to think of places in the neighborhood that could be interesting. And there's something inherently, deeply mysterious about that building. If you look online, there's like one sort of grainy photo of the inside, taken maybe as the door is closing. So I was intrigued by the mystery inherent to the building."

It took about three weeks to create the game, with most of that time spent illustrating it with his iPad and a program called Procreate. The action starts with an opening crawl that explains a bit of the backstory and the goal of the game: a service emergency is causing "severe delays" on all the lines.

"The mayor is baffled," the opening text reads. "Nobody can figure out what is going on." And the only way to fix the subway system and rescue the city is to figure out the controls inside the building. If you've ever played Myst, it's not too difficult to figure out you have to explore and poke around a bit to find all the various levers.

A photo of the start of the video game on 58 Joralemon Street

The opening of the game

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The opening of the game

Another cool aspect is the sound design: the eerie sound effects are taken from samples of Tupper's radiator, and he composed the rest of the ominous, synth-heavy background music himself as well. "The goal was to be kind of creepy and dripping," he said. "My dad sent me an email back—he's like, yes, after five minutes of playing it, I think I'm gonna go take a leak."

Asked about the secretive nature of the townhouse, MTA spokesperson Tim Minton said, "58 Joralemon is a vent and 'fan plant' that exhausts air from the subway below. There are emergency exits throughout the NYC subway system, and for security reasons we do not provide their locations."

As for the game, he added, "We have no comment on the game you described."

Ultimately, this is very much a first timer's video game, so don't go in expecting Red Dead Redemption: Brooklyn Edition: "It was really completely casual, and that was the only goal."

Of course, it's hard to be crazy-detailed when you don't even know what the inside of the place looks like. For what it's worth, New York Transit Museum curator Jodi Shapiro recently told Gothamist, "Honestly, it's really boring... It's just very industrial looking... a lot of structural ironwork in there."

But Tupper still hopes he can get a peek inside one day.

"I read that the neighbors rarely even see anybody go in," he said. "I would love a tour if anybody knows anybody—if anyone is reading this story, and knows somebody who knows somebody."