No Stone Unturned

The map's overall completion hitting 100% across every region - all collectibles (relics, documents, murals, monoliths, survival/coin caches), all Challenge Tombs, all challenges, all missions, every camp and tomb explored. Nothing is missable: fast-travel back after the story and use each region map's counters to hunt down what's outstanding. This is the big cleanup that rolls up most of the collectible achievements.