The setting of "The Cask of Amontillado" is in Italy during the carnival season. Even more specific than that, the bulk of the plot takes place in the vaults, cellar, or catacombs beneath the home of Montressor, the story's main character and narrator. The most important detail of the setting that contributes to the horror or suspense of the story is the fact that the two main characters, Montressor and Fortunado, are walking through a vault underneath Montressor's family mansion which holds the dead remains of his ancestors.
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