The Shards of Ironhaven are earned by defeating the guardians in each Grotto. Dungeon bosses hold maps to the grottos. If you think you are missing a shard of Ironhaven, try fighting the bosses in each zone. The Grotto doors are locked, and you must solve the Eldritch Riddles to open them. Be sure to read your quests carefully, because no hints are given as to the location of the things that will solve the riddles. The answers to the riddles can be obtaining items from enemies, fighting in specific locations, buying items in the shop, or killing certain enemies. There is a complete guide on our forums from other heroes who have tackled this quest.