I've been reading the Harry Potter books for years and there's something I noticed the other day which I can't believe I hadn't spotted before.
The Philosopher's Stone is hidden in some dungeons beneath Hogwarts. This is confirmed by Dumbledore.
"What happened down in the dungeons between you and Professor Quirrell is a complete secret, so, naturally, the whole school knows."
(Philosopher's Stone, Chapter 17, The Man With Two Faces).
Hermione also comments on how far the drop is after they fall through the trap door.
"We must be miles under the school," she said.
(Philosopher's Stone, Chapter 16, Through the Trapdoor).
So the Stone is kept in the dungeons. But the entrance is on the third floor. How does that make any sense?
The fall from the trapdoor is clearly not meant to kill or harm the intruder. So why not have the entrance in the dungeons themselves - or at least on the ground floor?
Surely that means a lot of architectural effort in rejigging Hogwarts. Harry, Hermione and Ron start off on the third floor and end up falling through the second, first and ground floors. Did they have to insert this chute into the middle of their ancient castle? Was it there by design? Or are we to suppose that this huge funnel running through the core of the building and a series of connected underground chambers were part of Hogwarts all along? It's a happy accident, if so.