Hogfather - Hub

At the Hub of the Discworld, the snow burned blue and green. The Aurora Corealis hung in the sky, curtains of pale cold fire that circled the central mountains and cast their spectral light over the ice. They billowed, swirled and then trailed a ragged arm on the end of which was a tiny dot that became, when the eye of imagination drew nearer, Binky.

He trotted to a halt and stood on the air. Susan looked down. And then found what she was looking for. At the end of a valley of snow-mounded trees something gleamed brightly, reflecting the sky.

The Castle of Bones.

***

Hogfather - p133