The Colour of Magic (Terry Pratchett)

THE LURE OF THE WYRM

It was called the Wyrmberg and it rose almost one half of a mile above the green valley; a mountain huge, gray and upside down.

At its base it was a mere score of yards across. Then it rose through clinging cloud, curving gracefully outward like an upturned trumpet until it was truncated by a plateau fully a quarter of a mile across. There was a tiny forest up there, its greenery cascading over the lip. There were buildings. There was even a small river, tumbling over the edge in a waterfall so wind-whipped that it reached the ground as rain.

There were also a number of cave mouths, a few yards below the plateau. They had a crudely carved, regular look about them, so that on this crisp autumn morning the Wyrmberg hung over the clouds like a giant’s dovecote.

This would mean that the “doves” had a wingspan slightly in excess of forty yards.