Aloy has plenty of Outfits in Horizon Zero Dawn, and most specialize in a particular type of defense. Only one Outfit is discoverable as a special, optional item, and it's the strongest one of all. The Shield-Weaver Armor is locked behind completion of the "Ancient Armory" quest. This guide will explain how to activate and complete the quest, obtain the various Power Cells, and claim your reward.
How to Activate the Quest
The Ancient Armory sidequest activates as soon as you pick up any Power Cell, or find the Bunker that holds the armor. Power Cells are littered throughout five separate story quests, which means you won't be able to entirely complete the sidequest until you're nearly finished with the game. Finding a Power Cell will set a waypoint that leads you directly to the Bunker, but if you want to find it on your own, look on the western side of the map near Devil's Thirst.
Inside the Bunker, you can see the Shield-Weaver Armor behind glass, protected by a panel with two Power Cells missing. You'll need to find those two cells, and then three more to unlock the armor from its restraints.
Power Cell Locations
As mentioned, the Power Cells are dispersed throughout story missions. You can obtain these anytime after completing those missions, but it's easiest if you keep an eye out for them while on the main quests themselves. That way, you won't have to backtrack, especially since many of these missions require some heavy platforming that's assisted by generous waypoints while in the story proper.
Ruins - The first Power Cell can be found in the ruins that Aloy discovered as a child. Once she's grown, and after having completed Womb of the Mountain story quest, you can go back to the Ruins for the Cell. You'll find a room with some various obvious treasure icons, but it's blocked by rock formations. Break them with your spear and head in to find the first Power Cell.
All-Mother Mountain - The second Power Cell can be found during the Womb of the Mountain quest, while Aloy explores All-Mother Mountain. Look for a locked bunker door and then turn left into a tunnel where the Power Cell sits.
Maker's End - When you reach the top of the Faro Skyscraper during a quest at Maker's End, you'll find a room with some major story revelations. In that room, look upward to find another path, and climb to the top for the next Power Cell. Then use the rappel hook to head back down the skyscraper.
Grave-Hoard - This Power Cell can be found in the main foyer of the Grave-Hoard ruins, on the ground.
Gaia Prime - During The Mountain that Fell quest, you'll come to a room with a hologram with another major story revelation. This one involves a major character speaking with a gathered group of scientists. The zipline leads out of the quest area, but rather than take it, look for a path that leads into a cave. Climb down it and find the final Power Cell.
With all five Power Cells in hand, you're ready to unlock your armor. Find the Bunker and insert the missing Power Cells into the red nodes that are empty. Then you'll have to move the nodes into the right positions to unlock the door. You can use your Focus to spot hints about the positions of the nodes, or you can simply refer to the solutions below, as read from left to right.
The solution to the door lock is: up, right, down, left, up.
The solution to the clamps lock is: right, left, up, right, left.
Once the clamps are unlocked, you can obtain the Shield-Weaver Treasure Box. Open it through your Inventory menu to obtain the outfit, as long as you have an open Outfit slot available.