Bank all items including runes (it will not let you enter unless you bank everything but the pebble and food. Bring Glarial's pebble, food, rope, Stamina potions and leave at least 2 open inventory spaces.Warning, there are several high level monsters in this dungeon
Go north-east of the large building where the book was found to find Glarial's Tomb. Use the pebble on it to enter.
Go through both paths of the dungeon, search the chest to find Glarial's amulet. (Pick-up an extra amulet or two by dropping it from your inventory and picking them up from the ground.)