Final answer:
Fortunato goes to the catacomb (crypt) with Montresor to taste a rare wine called Amontillado, but it is actually a trap for revenge.
Step-by-step explanation:
Fortunato goes to the catacomb (crypt) with Montresor because Montresor lures him there with the promise of tasting a rare wine called Amontillado. Fortunato prides himself on his connoisseurship in wine, and Montresor uses this knowledge to trick him. Once in the catacomb, Montresor seeks revenge on Fortunato for a thousand injuries and insults he has endured.