The heart of it
The Founder's Tower
A tower, a spiral stair, an observatory, a telescope, and one small light in a high window.
There is a light in the window of the Founder's Tower, and there has been every night for a hundred and fifty years. For sixty of those years, nobody at St Elowen's knew who was lighting it. The story of how we found out is told in The Star of Promise. The tower is no longer locked, and any girl may climb it on a clear evening, and look through the telescope, and see the light for herself.
The tower does not ask you for anything. It simply lets you go. If you would like the whole story, it is in The Star of Promise.