If you complete the following tasks the corresponding feature will become unlocked.
Unlock White Swimsuit: This outfit which is for use in the Mediterranean Sea level becomes available when you complete the game.
Unlock Treasure Hunt Mode: This feature becomes an available option at the 'Main' menu when you clear the game on any level. In Treasure Hunt mode you replay the game without having to complete the puzzles to collect the missing treasure.
Unlock Storyboards: Complete the game on the Master Survivalist difficulty setting.
Unlock Lara Croft Concept Art: Collect ALL the Relics.
Unlock Creature Concept Art: Collect ALL the smaller treasures in each level.