Shadow of the Tomb Raider has 9 Challenge Tombs in the story. None of them are missable. After the story you can continue to free-roam and work on 100% completion, for which the tombs are also required. Completing all challenge tombs unlocks the Tomb Raider trophy and achievement. They are the toughest puzzle sections in the game but also yield the best rewards. Each tomb unlocks one skill that cannot be unlocked any other way. At the end of every tomb is a statue (stele) that you can interact with for the bonus skill. Then you must exit the tomb, usually via a base camp fast travel point.

We'll go through them in chronological story order. Also, none of them require any special tools or gadgets. Once you reach an area you will already have all the things you need to complete the challenge tomb.