Indubitably, setting is the most important element of Poe's short story, "The Cask of Amontillado." With the ideal location for his nefarious plan of redressing the hyperbolic "thousand injuries of Fortunato," Montresor feels empowered in his design to lure Fortunato away from the celebrations of the Carnival and lead him through the labryinth of the family catacombs where no one will hear or learn about his deadly plan.
In addition, the structure of the catacombs with its narrowing passages and increasing niter affords the sadistic Montresor opportunities for increasing torture of his victim. For example, Montresor taunts his victim, knowing that he already has respiratory problems:
"The niter!" I said; "see, it increases. It hangs like moss upon the vaults....The drops of moisture trickle among the bones. Come, we will go back ere it is too late. Your cough--"
Then, as they traverse the chambers leading to where the cask of wine is supposed to be, Montresor takes Fortunato to a remote part of the crypt where human bones are piled up and thrown "promiscuously upon the earth," a sight which surely strikes fear in Fortunato.
After Montresor has Fortunato peer into an especially dark aperture, he surreptitiously fetters the man dressed in harlequin costume to the wall. Perversely, Montresor feigns continued concern for his victim's health. Clearly, the sinister setting of the catacombs fuels and abets the sadisitic nature of the narrator and worsens the chances for the feckless Fortunato.