Today’s the first day that Mac Kids is in our new home at 120 Broadway. We spent the past few weeks packing our work belongings in orange crates, preparing to settle into the Equitable Building in the Financial District, trading our beloved triangle for an H-shaped office (because what would Macmillan be without an unusual layout?). I still remember arriving at the Flatiron Building for my first day 10 years ago. I looked up at the building in awe, thinking, “I can’t believe I get to work there.”

Walking through the Flatiron Building was like traveling through a science museum that showcases different ecosystems—the rainforest, the desert, the tundra. In your office on the 7th floor, you’d be stripped down to a tank top, sweating, with the AC blasting even though it was full-on snowing outside. But travel to the 10th floor conference room, and you’d be covered head to toe, wrapped up in an actual blanket, shivering.

The bathrooms alternated by floor—men on even, women on odd—and we all knew which bathrooms to avoid (the ones so small you’d be bumping elbows with your boss on the way out), and the ones that a friend called “destination bathrooms” (11, with its large waiting area; 19, with a gorgeous view of the city). Those bathrooms were worth the elevator ride. And who knows, while you were waiting—which could take a while—you might run into Jill Biden, or Tyra Banks, or Jim Carrey.

At my first job at Macmillan, at Thomas Dunne Books, I worked on the 17th floor in a sectioned-off area we called “the annex,” but which I thought of as Narnia. No one could ever find me, because my desk was accessed through a door that not every floor had. Yes, every floor was different, giving the building a funhouse feeling as you wove left and right, searching for the conference room or the kitchen anew with each floor.

And each company felt as unique and as special as its floor plan. Mac Kids, where I work now, was a wonderland, with framed art crowding the walls, brightly colored board books packed onto shelves next to classics, and a sparkling energy fueled by employees whose early lives were shaped by books. Walk by one office and you may spy a menagerie of life-size zoo animals, painted freehand by a famous illustrator. Where else but the Flatiron can an artist paint on the walls?

There’s no experience similar to working in the Flatiron Building. We’d bemoan the lack of conference rooms, then brag to our friends that we got to work in that building. We’d complain about the fact that we needed our key cards to get from one side of the floor to the other, then we’d pour out of the doors at lunchtime to get burgers at Shake Shack, or a BLT at Eisenberg’s, or a flat white at Birch Coffee, a plethora of delicious (and affordable) options spread out in front of us like a glorified mall food court. We’d tell our authors, “Don’t get your hopes up, it’s not that nice inside,” then see their eyes light up as they took out their phones to snap a shot from the point office, with views that stretched all the way to Times Square, with the Empire State Building and the Chrysler Building so close you felt you could reach out and touch them.

That feeling I had on my first day in 2009 hasn’t gone away. I’ve felt it again and again over the past 10 years, the magic of seeing something from a postcard come to life in front of me. Farewell, Flatiron Building. You’re leaving a triangle-shaped hole in our hearts.

Kat Brzozowski is senior editor at Swoon Reads/Feiwel & Friends.