In Far Cry 6, there are several locked places that contain valuable weapons and supplies that you can steal from the army and use against them and free Yara with Libertad. For example, below the Cortina weather station in Costa Del Mar, you will find a bunker that contains the FND cache along with other valuable supplies, but is locked behind a sealed door. This guide describes in detail where to find the key to unlock the door and access the contents inside the bunker.
The key you want to find at his military site is on the east side of the base. Due to the chaos, we secured the base before we grabbed the key card, and we’re not sure if it fell from a remarkable NPC guarding the base or was on the crate. Regardless, head to the east side of the base and explore the containers there. Once you find the key card at the top of the box or rob it of a high-ranking guard, you can go underground.
The entrance to the underground part of the Cortina weather station is via the south-eastern part of the base, next to the pick-up point if you have captured the base. Go through the door and walk down the underground corridor. In these catacombs, you will not be able to enter any metal doors until you go down the stairs and find a locked door to your left. Next to it should be the inscription “FND Armeria”. You will be able to open the door using the bunker card and get the FND cache.