Hunted Demons Forge

You can get this one easy really early on in Chapter 1.1. After you and your partner cross a wooden beam high above the ground (E'lara makes note of this), the game informs you about special enchanted weapons in racks/cages that glow purple.

You will be able to see them from after crossing the beam, cross the platforms and simply walk around to the front, above the door is a sign being held by a piece of rope. Have either E'lara or Caddoc use their ranged attack on the rope so that the sign will smash through the door. Then just break the cages holding the weapons and equip them.

Sometimes the weapon drop won't be epic quality, if the achievement does not pop just reload checkpoint and try again. Congrats, easy achievement!

When you reach your first Chosen One in the first chapter(Dyfed) you will have to either get you partner to stand on the switch to the right of the Chosen one(If you are E'lara) or Stand on the switch yourself(If you are Caddoc). Get the person who is playing as E'lara to back track a little bit until they get to a pile of stuff thats on fire. Light your arrow on fire by walking up to it with your bow equipped(RT). Then go back and make sure your partner is on the switch. Shoot the fire arrow into the left eye. Once it is open sprin(A) down the large set of stairs. Dont worry about it being pitch black, nothing will jump out at you. One you reach the bottom there will be a chest in the middle. Dont open the chest yet. Instead, look to either the left or right of the staircase. You will see purple glowing thingys. Smash one of them and equip the weapon it drops to get this achievement.