Hotel between worlds

The door was completely ordinary. An old wooden door with a worn brass handle. You knew with absolute certainty that it hadn't been there a second ago. Beyond it should lie a familiar hallway, a street, an apartment—anywhere. But when you open the door, instead of the expected space, you find yourself confronted by a huge hall. The high ceiling disappears into the darkness. A burgundy carpet lies beneath your feet. Dozens of antique chandeliers hang suspended in midair, though none of them are attached to the ceiling. A massive clock hangs on the wall.
The hands show 03:17 *
The second hand doesn't move.
You take a step inside.
The door closes silently behind you.
— Good evening
A voice comes from behind the reception desk.
A man of about fifty stands there, wearing a perfectly pressed black suit. His silver hair is combed back, and a small badge with an image of a key gleams on his chest. He looks at you as if he is not at all surprised by your appearance.
— You're late
He takes the registration book from the counter and flips through a few pages.
— Although... - the man frowns. - Strange
He runs his finger across the blank page.
— You shouldn't be here
He is silent for a few seconds. Then a bell rings at the far end of the hall

• Ding *

The man slowly looks up. All the doors around him are opening. All sorts of people are peering out: a woman in an old-fashioned dress, a boy in a school uniform, a man in a silver space suit, an elderly man with a sword. And then one of the doors swings open of its own accord.

• Beyond it is complete darkness. *

The man behind the counter looks scared for the first time.
— No…
He quickly closes the register.
— This shouldn't be happening.
A voice comes from the darkness.

—* You're finally back. *

The man looks right at you.
— Anyway… welcome to The Last Door.
He hands you an antique key.
Engraved on the tag:

• #000

“And please,” he adds quietly, “don’t open the door at the end of the corridor.”
Pause.

• Especially if someone knocks from there first.