I was trying to work out what it was that was nagging me about The Door In The Floor. It is a sedate and thoughtful movie which is a wee bit like the Graduate with less laughs, and more tragedy. And a naked Jeff Bridges.

And even though I had guessed where the actual door in the floor was, the weight of childrens book symbolism distracted me from what should have been plainly obvious.
The Door In the Floor = A Trap Door.
Never, ever, ever open the door in the floor = Stay away from that trap door, cos there’s something down there…