Montresor finally leads him into the tunnels where the "amontillado" is at. Fortunato is lead into a tunnel with chains. So, Montresor chains him to the wall. Montresor starts panicking, because Fortunato starts to wake up, so he starts doubting that his plan will work.
Montresor finally traps him in the tunnel by building a wall of bricks. Fortunato wakes up and thinks it is a joke. But then, he finally realizes that he is going to be buried alive. So he finally accepts his fate and Montresor fills the last brick in to complete the wall.
You know that Montresor is telling the story, he says that he leaves Fortunado there to die. His tomb hasn't been messed with for 50 years.