How do you get to the next level in Arkham Asylum?

Use your grapple hook on the gargoyles around the room to get behind Zsasz and then jump on his back. These buttons should show up on your screen telling you what to press

Its not exactly called level. Its just a single story that goes on and on.

Switch on your detective mode (press x if you are using PC). Look up at the gargoyles (Animal statues near the roof). Once you do this according to the story batman then scans it and finds out that he can grapple over it. The game would not give you instructions of the controls from this point.

grapple up to this gargoyle. Once you are up the first one, grapple to the next. Once you are there, there are many ways to take him Zaas down.

- the easiest way is make batman face Zaas. the came would give a suggestion to glide kick. select this option. batman would glide towards him and hit him. he would be down for a few seconds. before he gets up you should do the "ground take down"

- another way is you can throw a batarang at him. he would fall down for a while. before he could wake up, jump off the gargoyle and glide towards him. once you reach him you can go the ground take down.

- yet another way which is the hardest but the fastest is, you can straight glide right behind him. you need to be very careful to never be seen by him and so don't go in front of him. from behind you can either do a scilent take down or punch him three times.

You have to propel yourself onto the gargoyles set up above him until it tells you to do a dive attack onto him, ending his reign of terror