At the top of the stair
The Observatory
A telescope, a window, and a lantern. So they say. Nobody now at the school has been up.
There is an old plan of the house in the Library, drawn in the Foundress’s own time, and at the top of the tower it is marked, in a small neat hand: observatory.
A telescope, then, of brass, pointed at the Kentish sky. A window. And the lantern, which everybody has seen from below and nobody has ever seen from beside.
That is what the plan says. The plan is a hundred and fifty years old, and the door is locked, and so the honest answer is that the school does not know what is up there now, and has not known for a very long time.
Something is. The light says so, every single night.