There’s a giant wooden door in the South End. Here’s what’s behind it

The mysterious wooden door on Berkeley Street on the border of the Back Bay and the South End.David L. Ryan/Globe Staff/Globe Staff

An unmarked door of any size can evoke a sense of mystery.

But a towering, weather-beaten, unmarked door — smack-dab in the middle of Boston — that looks like it could house the hulking mass of Daenerys Targaryen’s dragon Rhaegal? Now that conjures up more than a bit of wonder. It leads to some additional questions.

The Globe recently launched a new initiative asking readers to submit inquiries about strange/quirky/odd things around the city and state, curiosities that they’d like to learn more about and have us investigate.

The topics are put up for a vote. The first question readers wanted answered came from Ed Lyons and had to do with a massive wooden door that sits just beyond the border of the Back Bay, in the city’s South End.

“What is the weird enormous door for that’s on Berkeley Street where Back Bay becomes the South End?” Lyons asked. “What is brought through there? Giants?”

The answer, it turns out, is not as cool as giants. And we got most of it with a simple one-line e-mail from officials in the know.

We could tell you right now. But what’s the fun in that?

To find out more about what’s lurking beyond the Westeros-like door, which is surrounded by zig-zagging brick patterns and topped by windows covered with black metal bars, we first decided to venture over to the South End and do some poking around.

The first thing apparent was that the enigmatic entryway is hard to miss — unless you’re one of the many people craning their necks and staring at a smartphone, in which case, you’ve likely never noticed it, despite the fact that the door has been there for decades.

Coming down Columbus Avenue recently on a crisp fall day, a Globe reporter could spot the door even before turning onto Berkeley Street, where it’s tucked against a four-story apartment building of similar aesthetic.

After briefly scoping out the large door, which is almost directly over the Massachusetts Turnpike, we noticed a smaller, less impressive door to its right, one that seems more fit for humans.

So, we did the only logical thing: We knocked.

Not surprisingly, no one answered. And in the time we spent standing outside, staring up at the larger door in question, not a single soul ventured in or out.

Next, we decided to ask the locals if they knew anything about what secrets are behind the entrance. Is it, as Lyons inquired, a place for mythical creatures of humongous proportions?

We stopped Meagan Hanley, 37, who was walking briskly by, head down. She said she passed by the door “probably seven times a day” but had never noticed it until now.

“When you live here, you just kind of walk and don’t really look up,” she said, a bit sheepishly. “So now I’m curious.”

She didn’t have an answer. But she had some observations.

“It’s very ‘Game of Thrones’-like,” she said, giving the door a quick up-and-down. “I don’t know. Maybe it’s an empty space, probably. I don’t know.”

She said she hoped there were “trolls” inside, and asked whether we had tried to open it.

We knocked, we told her, but didn’t dare try and turn the rusted door handle. The building doesn’t exactly appear to be Fort Knox, but the door is sealed by what looks like a household lock. Several security cameras are positioned right outside it.

Unsuccessful in gleaning anything from Hanley, we bothered 23-year-old Natalie Panes, who was walking a dog. She was also stumped.

“I haven’t noticed this door, honestly, at all,” Panes said. “Maybe it’s a church, or a storage warehouse of some sort?”

The door, seen from the first floor, it opens to two floors. David Ryan/Globe staff/Globe Staff

Eventually, after we tried to bother a few more pedestrians, Christopher Tuccolo, a Dorchester resident who lived in the South End for many years, nearly got us over the finish line.

“It’s a vent, right?” he said, referencing the space the door protects. “Like, for the trains?”

Bingo (kind of).

When the Globe first started checking into what lurks behind the door, an answer came quickly from officials at the Massachusetts Bay Transportation Authority, though the details were slightly vague.

According to the T, the building is the Orange Line’s Berkeley Traction Power Substation and was built with the opening of the MBTA’s Southwest Corridor project in 1987.

The top of the door, on the second floor, is framed by electrical equipment. David Ryan/Globe staff/Globe Staff

Power equipment for the MBTA, when needed, is moved in and out through the building’s front door — hence the gargantuan size.

The door, which is divided into sections and opens at the top and bottom, like a barn door, was designed to blend in with the neighborhood decor and historic architecture, though it arguably has more of a medieval style with its massive bolts and hinges.

While that certainly answered part of Lyons’s question, we still needed to know more. What kind of equipment are we talking about here? Because those doors aren’t small.

After a few days of playful pestering (at one point the T joked that it would call MBTA Transit Police when we told them we were lingering outside, hoping to get in), we scrounged up some additional intel.

Electrical equipment on the second floor of the Orange Line’s Berkeley Traction Power Substation. David Ryan/Boston Globe/Globe Staff

Here’s how the substation works, according to the T’s Engineering and Maintenance Department: “It takes primary AC feeds (mainly from South Boston Power Plant) and with large rectifiers converts the power to DC for distribution to 600V third rail and moves trains.”

The department added, it “also feeds some unit substations for station ‘house’ power.”

The large doors, the department said, allow for equipment replacement if necessary. However, they are not routinely used.

“We can access the right of way of the Orange Line,” transit officials added, “but it isn’t something we typically use to bring construction material in/out.”

Bradley Clarke, a local transit historian and president of the Boston Street Railway Association, said the large door is common to most older substations, “and at one time these substations were all over the Boston area.”

The reason for the door’s height and size, he said, is so cranes and large moving equipment can access the substation’s components, parts that are “extremely large and heavy.”

No dragons. No giants. No factory of trolls.

Like the door, this case is closed.

Have you seen something out there that you’d like answers to? A giant door? Or perhaps a graveyard of rocking horses, strange stone marker on an island, or old trophies under a bridge. Let us know by filling out this form. If your suggestion is picked, we’ll check it out for you.