Poe is a master at using imagery—description employing any of the five senses of sight, sound, taste, touch, and smell—to create a mood. He does this as he describes the catacombs.
Because we have long been a visual culture, most writers rely on images we can see in our mind's eye, so I will first focus on Poe's more unusual use of sound imagery in this story. Near the end, as the chained Fortunato realizes he is being bricked into a crevice in the catacombs to die, he starts to scream. Montresor joins him, and their screams compete until Montresor's overcome Fortunato's. Fortunato then grows silent. Poe describes it this way:
A succession of loud and shrill screams, bursting suddenly from the throat of the chained form, seemed to thrust me violently back. For a brief moment I hesitated—I trembled. ... I replied to the yells of him who clamored. I re-echoed—I aided—I surpassed them in volume and in strength. I did this, and the clamorer grew still.
There is something particularly eerie about the loud, competing screams echoing over and over in the chilly catacombs—and something even more eerie about Fortunato's sudden silence. It seems it would terrifying to stumble by accident into the catacombs and hear those shrieks, and terrifying to hear them suddenly stop.
Other eerie touches include the black silk mask Montresor wears, which hides his face just as his flattering words hide his intentions.
The dark, narrow passages of the bone-littered catacombs with damp walls, lit only by Montresor's flaming torch, are also eery, and lead us to wonder what will happen in that isolated setting.
We then not only see but feel the cold and damp as Montresor stops, takes Fortunato's arm, and describes the scene before them, especially the nitre on the walls:
It hangs like moss upon the vaults. We are below the river’s bed. The drops of moisture trickle among the bones.
The above too is an eerie image that might lead us to think Fortunato would do well to take Montresor's advice and head out of the catacombs.