The dark and terrifying mood of "The Cask of Amontillado" is created largely through imagery. Poe uses powerful descriptions to show the dark underground catacomb:
...a deep crypt, in which the foulness of the air caused our flambeaux (torch) rather to glow than flame.
At the most remote end of the crypt there appeared another less spacious. Its walls had been lined with human remains...
(Poe, "The Cask of Amontillado," eNotes eText)
This is no ordinary wine-cellar, but a crypt serving both functions. Instead of spacious rows of barrels and bottles, there are tight corridors and slimy walls, with musty air that threatens to extinguish the torch. Walking through the catacomb causes Fortunato to cough violently, and the space is so dark that even the torches themselves are insufficient to light the way. The environment couples with Montresor's constant litany of "revenge" to create a claustrophobic, sinister mood.
One of the primary ways in which Edgar Allen Poe creates a dark and foreboding mood in his story "The Cask of Amontillado" is through the use of setting. It is in the pitch of night that Montresor happens upon Fortunato and invites him back to his abandoned estate. From there Fortunato and Montresor wander deep into the estates' underground vaults filled with decaying bones, narrow passages, and dark damp air. This setting creates a strong sense of foreboding and foreshadows Fortunato's unfortunate end. From the darkness of night, Montresor and Fortunato descend into the deeper blackness of the vault surrounded by death and decay. Poe conjures an end to meet this ominous setting as Montresor chains Fortunato to a wall at the back of a cave and buries him alive. Ultimately, Fortunato is swallowed up by the darkness before he even dies as his voice trails off and he stops responding to Montresor leaving the reader to wonder if he has met a more sinister fate than even Montresor imagined.