Unlock the following concept art at the "Extras" menu by performing the corresponding tasks:
CONCEPT ART - HOW TO UNLOCK Creature Concepts - Collect all treasures. Environment Concept Art for Arctic Sea and Amelia Concepts - Successfully complete Arctic Sea Expedition. Environment Concept Art for Coastal Thailand and Alister Concepts - Successfully complete Coastal Thailand Expedition. Environment Concept Art for Croft Manor and Doppelganger Concepts - Successfully complete Croft Manor Expedition. Environment Concept Art for Med Sea and Amanda Concepts - Successfully complete Mediterranean Sea Expedition. Environment Concept Art for Mexico and All Men Concepts - Successfully complete Southern Mexico Expedition. Environment Concept Art for Ship and Natla Concepts - Successfully complete Andaman Sea Expedition. Environment Concept Art for Jan Mayen Island, Gear, and Artifacts Concepts - Successfully complete Jan Mayen Island Expedition. Game Flow Storyboards - Successfully complete the game on the Master Survivalist difficulty. Lara Concepts - Collect all six Relics. Zip and Winston Concepts - Successfully complete the Prologue.
Complete the game on any difficulty to unlock Treasure Hunt mode, which allows the game to be replayed without the puzzle completion requirements in order to collect any treasure missed in your previous playthrough.