The secret Shield-Weaver Armor is by far the best armor in Horizon Zero Dawn. The Shield-Weaver Armor protects you completely from a certain amount of damage until it flashes red. After taking cover, the armor recharges and you are invincible again.
Before you can pick up the Shield-Weaver armor you have to collect 5 power cells.
1 LOCATION: Ruins 00:03
Can be accessed anytime
2 LOCATION: All Mother 01:28
Can be accessed during "The Womb of the Mountain" or after "The Heart of the Nora"
3 LOCATION: Maker's End 02:18
Reached Main Quest "Maker's End"
4 LOCATION: The Grave-Hoard 03:36
Reached Main Quest "The Grave-Hoard"
5 LOCATION: Gaia Prime 05:26
Reached Main Quest "The Mountain that fell"
06:03 Check your side-quests and select "Ancient Armory", which leads you to the Ancient Armory Bunker where the Shield-Weaver armor is hidden.