You can access Light World via the menu button "Dungeons". There are several dungeons, but all of them are locked. Keys can be found on quests or in the gem mine. Additionally, the key to dungeon 6 can be bought in the magic shop while the key to dungeon 9 can be bought in the weapon shop. Access to dungeons also depends on character level.
When opening the Light World you will find all dungeons on the map. If you have opened it you will be able to see the next opponent, incl. level, class and assigned element.
Each defeated dungeon enemy gives a fixed number of XP as reward. In addition, you get gold, and with a 50% chance an item which can be an epic item. Exceptions are the 10th level of each dungeon or dungeons 15 and 19. Here, every enemy rewards you with a guaranteed epic item.
After each fight you have to wait for one hour. If you want to fight faster, you have to pay a mushroom!