What is the significance of the transition from street to catacombs in "The Cask of Amontillado"?

The significance of the transition from street to catacombs in "The Cask of Amontillado" is to heighten the suspense and create a atmosphere of uncertainty and fear.  Poe is a master at finding a way to frighten us when we least expect it.  He draws us into a story only to transition us into horror.  I don't care for straight horror.  I like the creative, unexpected horror that you find in Poe and in Sci-Fi like Twilight Zone.  

The ordinary, in "The Cask of Amontillado" suddenly becomes  horrific, when we realize that Fortunato is to be murdered, much more frightening than a simple slasher type murder. 

When Montressor brings Fortunato down into the Catacombs under the pretense of tasting a fine wine, this is ordinary.  What really awaits this hapless victim, is his merciless death.  What could be more horrific or frightening, certainly more so that a direct assault on the senses. 

The sneaky, deceitful murder is much scarier than the one that is clearly identified as a threat.  This is what Poe does for us in his work, he is subtle, lulling the reader into the story, then wham, he brings out the macabre and the reader is caught unexpectedly terrified.     

"My heart grew sick - on account of the dampness of the catacombs. I hastened to make an end of my labor. I forced the last stone into its position ; I plastered it up."