The suspense here is that Fortunato is being brought to the palace by Montresor and the suspense builds up because we do not know how his plan is going to be executed. In addition, Fortunato is drunk so he is not fully aware of what's happening.
Now there is anxiety because it gets intense when you know Montresor is bringing someone drunk to his cellar. This builds up suspense because usually it's common for people to get murdered in cellars and nobody would ever be informed about it.
Now the readers are most likely thinking about what Montresor is going to do with Fortunato because now they are in a room full of skulls. The readers could be thinking that he'll kill him there and it will be his death place because there are other dead bodies in the room. Montresor also steps in front of him to maybe "set up" his death trap.
In this scene, the readers would be thinking when it's going to happen because they've been walking for so long. They continue to walk and Montresor uses the Amontillado wine as an excuse to keep on walking. This suspense builds up because we don't know when it's going to happen.
Now that they've reached something different besides the ongoing dead bodies, now the readers will be wondering how the plan is going to be executed. The suspense for this scene is the how.
Moments after, Montresor chains Fortunato to the wall and doesn't reveal how he's going to kill him. It can vary from slitting his throat to just letting his body decay. This is another example of suspense as in how.