This achievement is rewarded for completing a side quest which involves finding the four pieces of the Artherium Crest and discovering the location of the legendary Aetherium Forge.
This quest can be started in two possible ways. You can either discover the location of Arkngthamz(thanks Bananaster) that can be found directly south east of Dushnikl Yal, the Orc stronghold in the south of The Reach. The other way to start this quest is to find the non-skill book called Aetherius Wars, that can be found within Fort Dawnguard on the ground floor, another copy can be found on the roof of the fort and others are scattered throughout the world. I am not sure entirely if one can be found within shops or the College of Winterhold yet however.
Once you read the book, you can directed to the aforementioned location. You will need to bring a crossbow or bow with you in order to advance through this location, or find one in your travels(there is a unique bow within that is pointed out to you. Upon entry you hear a woman's voice and a ghost of a woman appears telling you her story of her search for the legendary Aethetium Forge and her unfortunate demise.
You battle your way through this falmer invested cavern(the falmer here have unique hardened falmer armour) and progress throughout until you reach a puzzle near the end of the area. If you hadnt taken the journal from the dead woman not far from the entrance, you will have to use trial and error to solve the puzzle. There are two dwemer devices high up in the wall( I forgot the name of the devices) and three below. Hit the bottom left one first, then bottom right, top left, top right and finally bottom middle to unlock the doors and acquire a Aetherium Crest piece.
Upon the collection of this piece, the quest updates, pointing you to the locations of the other 3 pieces; one in the northern area of The Reach, one in Ralbathar and one in Mzulft Storeroom. Upon finding the four, head to the final map location and insert the crest.
The ground begins to quake for about 2 minutes and then you gain access to the location of the Aetherium Forge. Pass through this cavern to the end and battle several dwarven spiders and spheres and finally battle the dwarven centurion boss; The Forgemaster.
Obtain the ingots from the nearby chest and approach the legendary forge. There are three possible items that can be made from the forge; Aetherium Crown - Allows the wearer to have two active Standing Stone abilities at once, Aetherium Shield - When used, turns attacking enemies ethereal which makes it impossible for them to attack or be attacked for 15 seconds and Aetherium Staff - Summons a dwarven spider or sphere wherever the caster is pointing.
Due to there only been one Aetherium supply, only one item can be made and is therefore unchangeable. It is pointed out by the female ghost, that she doesn't know if there are any more Aetherium supplies anywhere, which suggests that there may be the chance of encountering more later on, but I can't confirm this for sure. After the conversation, the achievement pops.