In Kuwaq Yaku location in Shadow of the Tomb Raider you will find two crypts. The crypts are located on opposite sides of the location. Both crypts contain a large amount of raw materials, information about dialects and special secrets. One crypt is underwater and the other one is blocked by metal plates that can be destroyed with a shotgun.
By asking people in the city you will learn that in its south-western part there is a hidden crypt. It's located underwater, so access to it is quite difficult.
To get to the crypt you have to dive in a water reservoir and swim along the rocks. You will swim to the surface by the rocky regiments where you can climb.
There are many enemies in the water which will attack you if you approach too close to them. If this happens, you must quickly break away from their grasp. Each action of this type takes some oxygen away from you. It's a good idea to quickly find a place to breathe and catch a deep breath after each fight.
When you get out to the surface, move up on the rocks. You will find yourself in a semi-open space. The exit will be blocked by boards and materials, and in order to destroy them, you must pull out the arrow, set it on fire and aim at a pile of objects. This way the materials will burn out and allow you to pass through.
Go further and stay near the left wall. On your way there will be a mural with inscriptions in the QUECHUA dialect. Behind it there is a damaged bridge. If you stand on the boards, Lara will automatically fall. Your task is to avoid all obstacles that lie on the road.
At the very end of the road Lara will jump out and you have to use your pickaxe on the branch and jump to the other side. If you don't do this, the character will fall from height and then you have to repeat all sequence again.
Behind a dangerous road you will find a room with a sarcophagus. Here, you will find Nine Strides' Boots. They will increase the amount of harvested man-made resources from each source.