I need this for a book I’m writing. A lot of people know about the existence of the room I’m talking about, but almost nobody has access to it.
It would have to be well hidden or well guarded. Indiana Jones and Tomb Raider come to mind as well.
As many potential rooms as possible in as many locations as possible, and no way to distinguish the right one. Of course, rotate it regularly.
Some old palaces in Japan have “nightingale” floors that purposely squeak to keep people from sneaking in. Could be a security feature outside your room
Is it on display in the bottom drawer of a locked filing cabinet stuck in a disused lavatory with a sign on the door saying, “Beware of the leopard”?
More seriously, just make it an incredibly uninteresting door that no one even thinks about, which everyone thinks is like for plumbing or linens or something boring and irrelevant. Then paint the door in whatever Disney NoSeeUm color is most appropriate.
Simply put: it stinks, like bad. The room is hidden under the largest city in the land, only accessible by spelunking through vast distances of underground sewers that smell like decomposing waste. This smell-field ensures only the bravest and most dedicated adventurers ever travel to the room, and none who attempt it enjoy talking about it.
