Situational irony is when what happens is the opposite of what is expected. Situational irony runs throughout the entire story because Fortunato is completely unaware of the danger he is in. Fortunato expects to taste a rare wine, not to be murdered. He thinks Montresor is his friend and that Montresor is doing him a favor. Ironically, it is Fortunato who hurries Montresor towards the catacombs. Fortunato has no idea he is hastening toward his own death. As Montresor says:
Fortunato possessed himself of my arm; and putting on a mask of black silk and drawing a roquelaire closely about my person, I suffered him to hurry me to my palazzo.
Throughout their journey deeper and deeper into the catacombs, Fortunato continues to be completely unaware of the dangerous situation he is in. For example, when Montresor offers to take him back because of his cough, which is worsened by the dampness, it is Fortunato who insists on going forward:
"Enough," he [Fortunato] said; "the cough's a mere nothing; it will not kill me. I shall not die of a cough."
Again, we read the irony in Fortunato's words. He will not die of a cough. He will die of being walled up and left to starve--but he is completely unaware of what is soon to come.