[Mister Underhill]

I've always been partial to this one:

A long-tilted valley, a deep gulf of shadow, ran back far into the mountains. Upon the further side, some way within the valley's arms high on a rocky seat upon the black knees of the Ephel Dúath, stood the walls and tower of Minas Morgul. All was dark about it, earth and sky, but it was lit with light. Not the imprisoned moonlight welling through the marble walls of Minas Ithil long ago, Tower of the Moon, fair and radiant in the hollow of the hills. Paler indeed than the moon ailing in some slow eclipse was the light of it now, wavering and blowing like a noisome exhalation of decay, a corpse-light, a light that illuminated nothing. In the walls and tower windows showed, like countless black holes looking inward into emptiness; but the topmost course of the tower revolved slowly, first one way and then another, a huge ghostly head leering into the night.

The prof seems to really feel his oats when he's describing an evil setting.