1. Ruins where you fell in as a child. Break some stone spikes with your spear to get to it. Can be accessed anytime as an adult.
2. All Mother. Can be accessed during "The Womb of the Mountain" quest or during "The Heart of the Nora" quest in one of the side rooms and you have to crouch to get to it. If you miss it during the quest near the beginning, and you get to the point where the gates are locked, you will need to get most of the way to the end for the next quest to open up.
3. Maker's End. During Main Quest "Maker's End" when you get up as high as you are going to go, look for some climbing handles to get even higher.
4. The Grave-Hoard. During Main Quest "The Grave-Hoard" you will see this as you explore, it's hard to miss.
5. Gaia Prime. During Main Quest "The Mountain That Fell" you will come to a point where you are outside and have just rappelled down. Look around to the left for a wall you can climb and it will be up there.
The location you need to go to is on the right side of the map, your quest guide should lead you there. Getting the outfit itself requires two puzzles to be solved. The first is a military time puzzle.
That opens the door to where the armor is stored and another puzzle awaits in the back of that room, this one deals with degrees in a circle.