Diablo/Chamber of Bone

This mission is a constant throughout the game and you will always have to face it. At level 6, in the catacombs, you will find a Mythical Book. Read it, to learn about the Chamber of Bone. On the same level you will then find a staircase that will lead you to the Chamber of Bone (note: if you have not yet read the book this staircase will not be accessible).

Climb the stairs and proceed northwest. In this area you will find many skeletons, which shouldn't cause you any problems anyway. Wait before opening the door to the room with the different floor. To the right and left you will find two levers: pull them both. You might encounter some big horned demons in the meantime, but taking them out shouldn't be a big deal, the only thing to fear is their charge. By pulling these levers, two further rooms will appear to the northwest, where you can find many magical items in the chests. This side mission is one of the best opportunities in the game to improve your equipment. After clearing this area, open the central door, to reveal a room completely filled with skeletons (plus two Unseen). If you play as the Warrior, stay in front of the door to prevent the skeletons from coming out. In this way you can attack them one at a time. Draw your sword and start a long massacre. Luckily the skeletons are quiete weak and if you have some potions with you, you should take them out easily. If instead you are using the Rogue or the Sorcerer, you should use some spell that allows you to hit multiple enemies at the same time, such as Fire Wall, Lightning or Inferno. With these spells you should clear the room very quickly. Once you've cleared all the skeletons, head out the door at the back to reach the last room. Here you will find more horned demons. Ignore them and reach the Book of Arcane Knowledge at the bottom. By opening the book you will automatically learn the Guardian Spell, which will be launched automatically, attacking demons. If that's not enough, use your attacks. There is nothing more to do here, you can go back to the main level descending the stairs.

REWARD: Guardian spell (as well as many magical items and experience points)