Montresor's vaults are described as being dark, wet, and foreboding. Initially, Montressor carries torches down into the catacombs because of the extreme darkness of the vaults. Fortunato follows Montresor down a winding staircase until they reach the damp ground of the vault. Montresor then comments on the "white web-work" on the cavern walls. Fortunato then takes note of the "nitre" on the walls of the cavern. Nitre is another name for potassium nitrate, which is a white crystalline salt that is often used as fertilizer and a constituent of gunpowder.
As the two characters descend further into Montresor's catacombs, Fortunato mentions that the vaults are extensive. Montresor then comments on the numerous piles of bones, "casks and puncheons intermingling." Montresor also mentions that the nitre hangs from the walls like moss and tells Fortunato that they are underneath a riverbed. This information explains the dampness of the catacombs and indicates that the vaults are deep underground. The end of the vaults are described as a dark crypt, where the "foulness of the air" causes their torches to glow. Three of the walls are aligned with human remains to the ceiling, and there is a small depression in the back wall, where Montresor locks Fortunato inside as he gradually buries him alive. Overall, Montresor's catacombs are dark, extensive, damp, and filled with piles of human bones.