Dungeons are usually full of monsters of different kinds and some have generally straightforward puzzles that get harder throughout, but they’re never too challenging in the compulsory dungeons. There are however extra puzzles laying around in the same dungeons, solely accessible via hidden passages found outside. These puzzles are only necessary to solve if you want to complete the game 100%, but can also be helpful to the characters, yielding hidden weapons and armour that can't be bought from the shops.

Source: Cubed3