Tomb Raider: Underworld - Invincibility

One hit kills:
While playing, hold LT and press Y, A, Y, X, LB, B.

Reveal enemy health:
While playing, hold LT and press X, B, A, LB, RT, Y.

Concept art:
Complete the indicated task to unlock the corresponding concept art at the "Extras" menu.

Environment Concept Art for Arctic Sea and Amelia Concepts: Complete Arctic Sea.
Environment Concept Art for Coastal Thailand and Alister Concepts: Complete Coastal Thailand.
Environment Concept Art for Croft Manor and Doppelganger Concepts: Complete Croft Manor.
Environment Concept Art for Med Sea and Amanda Concepts: Complete Mediterranean Sea.
Environment Concept Art for Mexico and All Men Concepts: Complete Southern Mexico.
Environment Concept Art for Ship and Natla Concepts: Complete Andaman Sea.
Environment Concept Art for Jan Mayen Island and Gear and Artifacts Concepts: Complete Jan Mayen Island.
Creature Concepts: Collect all treasures.
Game Flow Storyboards: Complete the game under the Master Survivalist difficulty setting.
Lara Concepts: Collect all six relics.
Zip and Winston Concepts: Complete the Prologue.

White swimsuit:
Successfully complete the game. You can now opt to outfit Lara in a white swimsuit in the Mediterranean Sea level.

Treasure Hunt mode:
Successfully complete the game. Select the "Treasure Hunt" option at the main menu to replay the game without the puzzle completion requirements in order to collect any treasure missed in your previous playthrough.

Achievements:
Complete the following achievements to unlock Xbox Live Gamerscore points.

Prologue 25 points: Complete the Prologue.
Master Survivalist 100 points: Complete the game on hardest possible settings.
Treasure Collector 30 points: Find 10 Treasures.
Skilled Treasure Collector 40 points: Find 50 Treasures.
Dedicated Treasure Collector 50 points: Find 100 Treasures.
Master Treasure Collector 60 points: Find all 179 Treasures.
Relic Collector 30 points: Find a Relic.
Dedicated Relic Collector 50 points: Find 3 Relics.
Master Relic Collector 70 points: Find all 6 Relics.
Swan Diver I 10 points: In one adventure, swan dive off one of the three highest points over water in the game.
Swan Diver II 10 points: In one adventure, swan dive off two of the three highest points over water in the game.
Master Swan Diver 10 points: In one adventure, swan dive off the three highest points over water in the game.
Climber 5 points: Execute a chimney jump of at least 2 wall kicks.
Master Climber 10 points: Execute a chimney jump of at least 4 wall kicks.
Speed Demon I 5 points: Drive into Xibalba in under 45 seconds.
Speed Demon II 5 points: Drove from the top of Valgrind to the bottom in under 50 seconds.
Speed Demon III 5 points: Drive through the Valhalla Maze in under 40 seconds.
Master Speed Demon 10 points: Beat all three Speed Demon challenges.
Roadkiller 5 points: Kill an enemy by running over it with the motorcycle.
Master Roadkiller 10 points: Kill five enemies by running over them with the motorcycle.
Grenadier 10 points: Kill two enemies with one grenade.
Master Grenadier 10 points: Kill three enemies with one grenade.
Weapons Expert 5 points: Execute an Adrenaline Attack headshot on an enemy.
Weapons Master 10 points: Execute ten Adrenaline Attack headshots.

Additionally there are seven secret achievements.

Mediterranean Sea Expedition 50 points: Mediterranean Sea Expedition successfully completed.
Coastal Thailand Expedition 75 points: Coastal Thailand Expedition successfully completed.
Croft Manor Expedition 25 points: Croft manor Expedition successfully completed.
Southern Mexico Expedition 100 points: Southern Mexico Expedition successfully completed.
Jan Mayen Island Expedition 50 points: Jan Mayen Island Expedition successfully completed.
Andaman Sea Expedition 25 points: Andaman Sea Expedition successfully completed.
Arctic Sea Expedition 100 points: Arctic Sea Expedition successfully completed.