Strongboxes

Strongbox is a gameplay mechanic in the Survivor timeline. first introduced in Tomb Raider.

Tomb Raider (2013)
Strongboxes contain Salvage in much larger quantity than other sources. Lara can pry them open with her pry axe, and later climbing axe.

Rise of the Tomb Raider
Strongboxes make their return, most of them can be pried open with a climbing axe, while some must be lock-picked. Now they contain Weapon Parts, enabling Lara to use new weapons. Couple of crafting tools can also be found in Strongboxes.

Trivia

 * In Shadow of the Tomb Raider they are renamed to Treasure Chests.