About 5 minutes to read aloud.

The workshop had four walls that everyone could account for, and a fifth wall that nobody could. It ran along the back, past the shelf where the paint pots stood in their rows, and set into it was a door no taller than a broom handle, made of wood gone grey with age. There was no keyhole. There was no sign. There was only a small brass handle, worn smooth, as if a great many hands had turned it over a great many years.

Tinsel was the newest elf in the workshop, three weeks into the job and still learning which drawer held the small screws and which held the smaller ones. She had asked about the door on her first day.

"Nobody built it," said Bramble, who had been carving rocking horses since before Tinsel's grandmother was born. "It was here when the workshop was here. That's all anyone knows."

"Does it open?"

"Never seen it open. Never seen anyone try."

That struck Tinsel as a strange thing for a workshop full of curious people to have simply agreed not to do, and she thought about it on and off for three weeks, the way you think about an itch you have decided not to scratch. Then came Christmas Eve, the one night the workshop stood empty and quiet, every sledge loaded and gone, every elf sent home to sleep before the great clear-up in the morning. Tinsel had stayed behind to finish a train she was painting, and when the last lamp but hers was out, she found herself standing in front of the small grey door with her hand already on the handle.

It turned easily, as though it had been waiting to be asked.

Beyond it was not snow, and not the yard, and not anything Tinsel had a name ready for. It was a room, low-ceilinged and warm, lit by a single lamp, and every wall of it was hung with tools. Not the tools from the workshop bench. Older ones. A plane with a handle worn into the shape of a hand that was not her own. A set of chisels laid out on a cloth gone soft with use. A ledger, thick as a brick, open on a stand in the middle of the floor.

She stepped in without quite deciding to. The ledger's pages were covered in handwriting, hundreds of hands, she thought, going back further than any date she recognised, each one a note about a toy or a mend or a small repair made in the night. Near the bottom of the open page, in ink still faintly wet, was a line about the very train she had left drying on her own bench, the joints she had not been sure she had got right.

"It records what gets made," said a voice behind her, unhurried, unsurprised to find her there. Santa stood in the doorway she had come through, though she had not heard it open twice. "Every workshop needs a room like this one. A place that remembers what came before it, so the ones working now do not have to carry it all themselves."

"Nobody told me it was real."

"Nobody could. You had to open the door yourself, or it would only ever have been a story someone told you." He looked at the ledger, at the fresh line about her train. "It seems to have been expecting your work rather sooner than I expected your curiosity."

Tinsel laughed, and the sound of it sat oddly in a room built for quiet. She looked once more at the tools on the walls, the worn handles, the soft cloth, and then she stepped back through the little door into the workshop she knew, where her train stood exactly where she had left it, the paint dry at last, the joints, she found when she checked them, entirely sound.

She left the door as she had found it, unlocked, unlabelled, and closed it gently behind her.