As an action rpg game, the combat is very important. But not only enemies and bosses are challenges to overcome. The game is complemented with additional puzzles to test your mind.
All of this puzzles can be solve in a logical way. There are lots of information spread across the levels in books, papers, notes, etc. This information can tell you what you need or how it works a mechanism/puzzle in particular, giving some clues.
For example, there's a locked door blocking you the way to the boss. Aside from the door, there are five lever switches. You remember reading some note before telling that this switches control the door and the only way to open it is with the right combination (UP/DOWN) of the levers.
For hinder this puzzle a little more, one of the switches don't have a lever. You need to find something to replace it. Looking around/looting from enemies, you find two items, a metal bar and a metal grip. This items alone doesn't work, but you can combine one item with the other to create a new item, a lever.
Once you got the lever, you can use it on the empty switch and start to solve the puzzle trying different combinations. Even some notes can tell you the right position of one or two switches if you have read it before.
A lot of the puzzles in this game requires item finding and combining with the right ones to create the item you need to solve th puzzle and advance through the game. All this can be done inside the inventory.