Diablo/Arkaine's Valor Armour

At catacombs level 5, read the Book of Blood that will tell you about fountains, bloodstones and other things. Simply go through the door and beware of those fat ones. Kill them and grab the bloodstone, then put it on the pedestal. Do it two more times until the pedestal holds three bloodstones.

A wall will magically disappear and a hell will be shown to you. Go through it and kill more fat demons. On the floor you will see the unique item: Arkaine's Valor Armour. This armour is pretty good at the beginning, since it gives nice magical bonuses.

Before finishing the quest, if you go back to town and speak with the townsfolk, they will tell you that Arkaine was a noble warrior from Leoric's navy.