Dungeons originally refer to the underground prison in middle age castles. However, in RPG games, dungeons are labyrinths that the player character need to adventure through in order to find in-game items that helps them on the journey. So in later RPG games, dungeons don't necessarily need to be underground, nor do they need to be prisons. The varies from mines, castles, underground cave system, mountains or even on the clouds. Usually at the end of a dungeon, there is a boss to fight.

Here are a list of dungeons appears in the Ys series: