Not Terry Pratchett's but my own.
While driving to my cousin's house yesterday, the sun was setting and, since my cousin lives west of me, in my eyes. But it gave me an idea for a campaign world:
The world is flat. It is a disc. The "sun" never rises into the sky and sets beyond the horizon but literally rolls through a groove at the edge of the disc in a never-ending circle. There is no true day or night on the disc. When the sun is passing closest to you, it looks like the bright mid-morning sky. When the sun is directly opposite you, it looks like the darkness of dusk. But at all times there is just enough light to not be dark.
More later. I have to go to work.