After his trial, the narrator first finds himself imprisoned in total darkness inside a small cell. "The blackness of eternal night encompassed me." Being confined is, itself, frightening for the narrator--"[T]he atmosphere was intolerably close,"-- but his terror is increased when, having moved along the damp walls in order to determine the size of his cell, the narrator secondly discovers that there is a hole in the floor.
After the narrator trips over a remnant of cloth that he has used to mark the beginning of his walk around his cell, he discovers a startling circumstance: While his chin lies on the floor of the cell, his
...lips, and the upper portion of my head, although seemingly at a less elevation than the chin, touched nothing.
At the same time, the prisoner feels a "clammy vapor" on his forehead and he smells "decayed fungus." When he puts out his arm, he discovers that he has fallen at the very edge of a circular pit. Breaking off a small fragment of masonry just below the margin of the hole, the prisoner drops it into the pit only to realize that it is a deep pit filled with water. When there is a rapid opening and closing of an overhead door, the narrator "saw clearly the doom which had been prepared for me." He congratulates himself on escaping this deadly accident by his timely fall.