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.
An underground catacomb, somewhere in Italy, during the carnival season
The setting in “The Cask,” and in most Horror or Gothic Fiction, has a special purpose: to suggest freedom or confinement, in harmony or opposition to the freedom or confinement of the characters. This is called the “Gothic Interior.” Most people go back and forth between feeling free and feeling trapped. The Gothic Interior is meant to make us hyperaware of these emotions through careful attention to the setting.
When we look at the settings of “The Cask,” we can see that the story has a distinct movement from freedom to confinement.
First, let’s start with the country. Italy doesn’t directly factor into this formula of the Gothic Interior, at least not in an obvious way. It might have something to do with the guy who wrote the first explicitly “Gothic” story, The Castle of Otranto: A Gothic Story. That guy is Horace Walpole, and when he first published Otranto, he claimed that it was a translation of an old Italian manuscript he found. When the story became a huge success, he confessed that he wrote it himself.
Not so coincidentally, Otranto has much to do with freedom and confinement. In a nutshell, it’s about a giant gold helmet falling from the sky and trapping a guy underneath it. So, the Italian setting is probably Poe’s nod to Walpole.
The carnival season and the Montresor family catacomb are a bit more direct. The carnival is a literal celebration of freedom, which both Montresor and Fortunato are participating in at the beginning of the story.
As they journey through the catacomb, Montresor and Fortunato move into smaller and smaller − and fouler and fouler − spaces. This suggesting that, as they travel farther away from fresh air, they are also moving further away from freedom.
Fortunato is eventually trapped in a space that represents the opposite of freedom: he’s chained up and bricked inside a man-sized crypt with no air and no way out. You can certainly argue that Montresor presents a contrast to Fortunato’s fate in that he finds freedom at the end of the story: he is alive.
Montresor is free to do as he wishes. Ironically, what he wishes to do is tell this story. Which means that the story has him trapped. He can’t forget it, and he has to talk about it. In his mind, he’s still down there in the hole with Fortunato.