Strongboxes
Strongboxes are a kind of Secret in Tomb Raider (2013) and Rise of the Tomb Raider. They can be found all over Yamatai and Siberia. Strongboxes are big metal crates that are locked and can not be opened without a tool.
Tomb Raider (2013)
In Tomb Raider 2013 Strongboxes contain a huge amount of Salvage. They are grey and Lara has to use her Axe or the Old Pry Tool to open them.
Rise of the Tomb Raider
In Rise if the Tomb Raider they contain Weapon parts. Collecting three parts of the same weapon will unlock an new weapon. They are red and again Lara has to use her Axe to open them. Some Strongboxes are more secure; here she has to use the Lock Pick she acquires in the Mission Communications Breakdown.
Gallery
Lara opening a Strongbox in Tomb Raider (2013)
...in Rise of the Tomb Raider using her newly acquired Lock Pick
