The Aetherium Forge. The Aetherium Forge is a located beneath the Ruins of Bthalft and only accessible once all four Aetherium Shards have been assembled to form the Aetherium Crest.The over 4000-year-old forge is guarded by by Dwarven Constructs, including The Forgemaster.he Aetherium Forge. The Aetherium Forge is a located beneath the Ruins of Bthalft and only accessible once all four Aetherium Shards have been assembled to form the Aetherium Crest.