In the Light and Shadow Worlds (can be accessed via the menu button "Dungeons"), there are 28 dungeons each in which monsters are waiting to be defeated in battle. In addition, at certain points of the game progress some special dungeons will be unlocked (Demon Portal, Tower, Twister and Continuous Loop of Idols) which can also be accessed from the same menu.
At the beginning you can only enter Light World. You can unlock Shadow World later.
To enter a dungeon, you must find the appropriate key first. Usually you find keys on quests. Certain keys can also be bought in the weapon or magic shop, found in the gem mine or found as a result of previously completed goals and tasks.
In the game content overview you can find information about the conditions that must be met to unlock a dungeon.
Rewards for defeating a dungeon enemy include XP, gold and, with a 50% chance, items which in turn can be epic items with another 50% chance.