When you start the game, you find yourself jumping across a bridge chased by trolls.

Do all of the parts of that level until you reach the part with the giant armored sleeping troll.

You will notice that there are chandeliers on the ceiling.

Without falling into the room wake up the troll and aim at the chandeliers with Chilla's ice spike.

The troll will collapse (if you aim right) and open the gate

If you miss you will either try to get him to go to another or use the Pummel Weed/Chilla combo.