The setting of this story may be its most unforgettable element. What are some of its most horrible details?

The torture chamber in which the narrator finds himself in "The Pit and the Pendulum" has multiple horrors. Here are six:

1. Utter darkness: When the narrator first wakes up in the cell, he finds that "the blackness of the eternal night encompassed me," causing him to gasp for breath.

2. The pit: When he encounters the pit, he is unable to see it. He drops a pebble down, and it falls for about a minute before he hears it splash in the water. The fact that he would have fallen into it if he had not tripped on his robe is petrifying; the thought that there may be more than one pit in the chamber is worse. 

3. Decoration: Later, when he can see, he notices the horrible figures of fiends and skeletons drawn on the walls, and when the walls heat up, they become very bright in color and even scarier.

4. The pendulum: This torture device is terrifying, and part of its terror is that it moves so slowly that the character has time to contemplate his oncoming doom.

5. Rats: Rats are constantly swarming about him when he is strapped to the table, and when he spreads the food on his bonds, hundreds of them are crawling all over him, making "a disgust, for which the world has no name, [swell] his bosom." 

6. The walls: After he escapes from under the pendulum, the walls begin closing in on him and heating up until they are just about to force him into the pit.

The torture chamber designed by Poe is certainly one of the creepiest settings in literature.