The following page contains the description of unlocking the bronze trophy Resting Places in Shadow of the Tomb Raider. The achievement is awarded for learning the secrets of any three crypts.
During the game you can explore optional crypts. They appear on the map after you are near them or after you learn about their existence (e.g. from the map or from NPCs you meet). After reaching the marker on the map you have to start exploring the optional crypt. It is worth mentioning here that some crypts are initially unavailable and Lara must acquire new equipment (e.g. a winch or a shotgun).
Crypts can be found in the following locations - Peruvian Jungle, Kuwaq Yaku, Hidden City, and San Juan Mission. Explore any three of those to get the trophy.
Detailed description of all crypts and relevant walkthroughs (puzzle solutions, trap layout etc,) can be found in the chapter dedicated to Crypts. A crypt is considered fully explored once you reach the sarcophagus - an example is shown on the picture above. Lara needs to open the sarcophagus and collect the loot.