Shortly after entering the ruins, one hears the voice of the deceased explorer Katria telling the Dragonborn to turn back. As they cross a gap on the side of a fallen pillar, Katria appears and explains that she had been pursuing a Dwemer Aetherium Forge that was capable of making such powerful weapons that it drove the Dwemer into civil war.
Katria tells of how she died while attempting to find the lost forge. The Dragonborn can opt to enlist Katria's help while delving through the ruins, which experience periodical earthquakes causing bits of the ruins to fall apart, while plenty of Falmer jump out of their holes in the canyon walls.
Katria will remark that a there is a chest behind a sealed gate. From the gate, go west and jump down the series of ledges until arriving at a stream. Going upstream eventually leads to the chest and a lever that opens the gate. If you continue upstream until you get to a pool of water. Dive about halfway down you will find a cave. Follow this underwater cave to the end to find a chest, weapon, and shield.
As they make it near the bottom of the ruins, Katria points out her lost bow (Zephyr with 30% extra shooting speed), which will be needed to complete the puzzle later on if one does not have a bow on hand. Finally reaching the bottom, one finds a set of 3 locked doors with a large Dwemer head and 5 tonal resonators above the three doors. There are 5 tonal resonators which must be hit in correct order in order to open the doors. If hit in the improper sequence, traps will trigger which include explosive arrows, dwarven spheres, dwarven spiders, as well as a centurion. The resonators are arranged in two rows; three on bottom, two on top. The correct order is bottom left, bottom right, top left, top right, bottom middle. After the doors open, the player can enter the treasure room that contains the first of 4 Aetherium keys used to activate the lost Dwemer forge.
The location of the other three Aetherium pieces are clearly marked in Katria's notebook, which can be found on her body at the entrance of Arkngthamz where she first appears.
Once all four pieces have been assembled, the Dragonborn can use them to gain entrance to the Aetherium forge. At the bottom, in the forge room, one must fight 15-20 dwarven spiders, dwarven spheres, and the Forgemaster, a leveled Dwemer Centurion that expels fire rather than steam. Completing the quest allows the Dragonborn to choose from one of three unique Aetherium items.
- 4x Centurion Dynamo Core
- Aetherium Shard
- Several glowing mushrooms
- Ebony ore vein - on the right wall of tonal resonator room, at base of a ledge.
- Quicksilver ore vein - on a ledge above the ebony ore vein, along with an unopenable dwarven chest.
- Outside of Arkngthamz, the Dragonborn may experience small tremors. That's because Katria got the combination of the tonal resonators wrong thus causing an earthquake.