The Grand Stairs is the first of six 6-man instances in Moria where the reward is Moria Medallions. These medallions can be turned in at your class trainer for better gear, or eventually for relics. You can get seven medallions a run whether you run hard mode or do a full clear (recommended for those with quests). It takes 100 medallions in all for the full teal set of gear and about 18 for the class specific purple set.