You enter the Crusader Helmet Quest and fight about 3 Giant Spiders (more, if lured). After that, you turn to a path that goes straight south, and fight at least 1 Giant Spider. After you kill the Giant Spider, keep going south, until you reach a dead end, which then you spot a door and cannot open it unless you're at the part after talking to Kroox. Once you open the door and chest you will see the message in green "You have found a dwarven armor", and there you go. You have just won your prize.