Two Doors, One Vanishing World

I thought about my flat. The three years of it. The known creaks, the reliable boiler, the water stains I could map from memory. I thought about the eleven-inch frame in an eight-inch wall, and the warmth of the handle, and the fact that the door had appeared for me and not for the forty other people who passed this corridor every day.
I stood there a long time.
Then I closed the door, went upstairs, and knocked on flat 38 again.
Adanna answered with her coat on.
We looked at each other. We didn’t need to explain. We had reached the same place by different routes, the way parallel lines will eventually meet if the geometry of the world bends the right way.
We each went back to our own door. We each opened it. We each stepped through.
I have tried many times since to describe what it felt like to cross that threshold — the brief sensation of the frame around me, the shift in air pressure, the moment when the hallway carpet became hillside grass under my feet — but language keeps failing me at exactly that point, like a road that simply ends at a cliff edge. What I can say is that the grass was real. The wind was real. The city below was real, and it was full of people who were not quite people, with eyes that caught the double moonlight in ways human eyes don’t, and hands that moved when they spoke as though the gestures were part of the language.
We stayed for what felt like weeks. We found each other on the hillside, which surprised neither of us.
And then, when it was done — when we had learned what we had apparently been brought there to learn, or given what we had apparently been brought there to give, though I am still not entirely certain which it was — we found ourselves back. Both of us. Standing in the second-floor corridor of the building on Ashveil Lane, the carpet under our feet, the boiler distantly complaining somewhere below.
The wall was magnolia again. Scuffed at knee height. No door.
I checked this morning, as I said. Adanna checked hers. We texted each other the same word at almost the same moment: gone.
She has invited me for tea. I said yes. We will sit at her kitchen table, in the ordinary kitchen with its ordinary wall, and we will not talk about what we learned or what we gave or which of those it was. We will just sit with the knowledge of it, the way you sit with something that has changed the shape of the room without moving any of the furniture.
Outside her window, in the alley below, a single lantern burns. Green flame. It was not there yesterday.