One of the symbols that occasionally haunts horror and dark Gothic literature is that of the evil shape. It's been a while since I've read any Lovecraft, but I think he uses it occasionally. Here's the closest thing I've ever found to something that really has an evil shape. It's perhaps not quite up to 'evil'; but I think most people think of it as a bit creepy.
This building would make a great metaphor for a Kafka-esque story, with its wickedly slanted walls, it's tall brooding emptiness, it's visibility to an entire city, the refusal of the citizens of the city even to acknowledge its presence.
Hmmm. My literary wheels are starting to turn.
(Extended Hat-tip: From The Shape of Days, via Marginal Revolution, via Under the Sun.)