Get to the room in the Cursed Cave where you must throw the skeletons into the barrier. Do not throw them. Instead, just kill the skeletons. They will keep respawning and you will be able to gain as many levels as desired.
Go to the front of the place where you are fighting. You will not get hit by the lava coming at you. Keep pressing Square when the enemies appear.
In the Ruined City of Adoni, there is an easier way of defeating the tortured zombies. Pressing Circle (jumping) and X (a downward slashing attack) will inflict 90 percent damage.