The level cap for your first playthrough is 22, although upon starting a new game, experience previously earned is added. If you have high-quality equipment, you can farm experience to reach level 30 after progressing until the Soul Arbiter's Maze is available. This happens after you acquire the Interdiction ability and the quest to find Judicator. The mini-Boss enemies on floor 10 are the only ones to give experience, with the Bone Giants giving the most.