There are 26 documents, 18 relics, 21 survival caches, 9 coin caches, 14 strongboxes, 12 murals, 2 crypt treasures and 3 challenges with a total of 24 locations. 21 of them are in the 3 tombs, the tomb videos are separate (look in the fourth post) but at the right places I put a link in the video. So there are 126 collectibles locations in Soviet Installation. You obtain this skill in the first available sidemission in the Soviet Installation area called 'Communications Breakdown'. Some collectibles require the lock pick skill.

Don't worry, you can get all the collectible achievements after you completed the game. You can only go back to the Syria area AFTER you have finished the game. I recommend you play the game, enjoy the story and the great game and at the last basecamp (point of no return warning) you go back and collect all collectibles in all areas. In some areas you can collect all collectibles on your first visit but in most areas you have to come back later to collect all collectibles because you have not the ability or the gear to collect all of them on the first visit. With the Y button you see the challenges. When you push the back button on your controller you have an overview for the area where you are. The game has a total of 394 collectibles and 18 challenges which have 109 locations, so we have in total 503 collectible locations in the game. Welcome to my collectibles guide for the game Rise of the Tomb Raider.

Rise of the tomb raider collectibles