Hogfather - Stairs

What threw the eye was the absence of shadows. You didn't notice shadows, how they delineated things, how they gave texture to the world, until they weren't there. The white marble, if that's what it was seemed to glow from the inside. Even when the impossible sun shone through a window it barely caused faint grey smudges where honest shadows should be. The tower seemed to avoid darkness.

That was even more frightening than the times when, after a complicated landing, you found yourself walking up by stepping down the underside of a stair and the distant floor now hung overhead like a ceiling. He'd noticed that even the other men shut their eyes when that happened. Teatime, though, took those stairs three at a time, laughing like a kid with a new toy.

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Hogfather - p81