The NPC will give you the trinket Guide of Antanas, which you must equip to complete the quest. Once equipped, head up towards the gate you opened near the Injured Monk and out into the bridge with the three infested enemies. After dealing with them, check the sides of the walls for faded runes that you can now interact with by pressing triangle. Activate the symbol and continue forward towards the area where you obtain the Gauntlet. Look to the sidewall of the stairs and activate a second rune, then a third on the other end of the gauntlet bridge.