Levels are the various environments where you play throughout Castle Crashers. Each chapter lists a certain group of levels which the player must complete in one session, in order to reach the next chapter and allow the game to save progress. For example, if you complete the Forest Entrance and the Thieves' Forest levels, and then close the game, the next time you open it, you will have to play through the Forest Entrance and the Thieves' Forest again, and keep playing through the rest of the levels in that chapter until you defeat the Catfish. If at that moment you turn the game off, the next time you open it, you will already have access to the first level of the next chapter, which is Tall Grass Field.
- Note: The above rule only applies when turning the game off. Just exiting to the world map will still allow you to keep playing in the last level you were in. This is useful for when you have acquired some skill points while playing through a level and you want to allow them in your attributes at that moment.