Discworld – Maskerade (Terry Pratchett)

It wasn't exactly a secret. When the room had been divided a space had been left between the walls. At the far end it opened on to a staircase, a perfectly ordinary staircase, which even had some grubby daylight via a dirt-encrusted window.

Agnes was vaguely disappointed. She had expected, well, a real secret passage, perhaps with a few torches flickering secretly in rather valuable secret wrought-iron holders. But the staircase had just been walled off from the rest of the place at some time. It wasn't secret-it had merely been forgotten.

There were cobwebs in the corners. The cocoons of extinct flies hung down from the ceiling. The air smelled of long-dead birds.

But there was a clear track through the dust. Someone had used the stairs several times.

She hesitated between up and down, and headed up. That was no great journey-after one more flight it ended at a trapdoor that wasn't even bolted.

She pushed at it, and then blinked in the unaccustomed light. Wind caught at her hair. A pigeon stared at her, and flew away as she poked her head into the fresh air.

The door had opened out on to the Opera House's roof, just one more item in a forest of skylights and airshafts.

She went back inside and headed downwards. And became aware, as she did so, of the voices…

The old stairs hadn't been totally forgotten. Someone had at least seen their usefulness as an airshaft. Voices filtered up. There were scales, distant music, snatches of conversation. As she went down she passed through layers of noise, like a very carefully made sundae of sound.