Here is the full list of all 27 The Cave achievements worth 400 gamerscore. It takes around 12-15 hours to unlock all of the achievements on Xbox 360.
Took all characters to the bottom of The Cave. (Player 1 only)
Saw every character's "bad ending". (Player 1 only)
Played some dubious role in the Monk's murder of his Master.
Saw someone slip off a ledge in the Missile Silo.
Saw a postcard returned to the Gift Shop.
Saw every Can of Corn in The Cave destroyed.
Recorded and played back the elevator music from the Zoo food court.
Served as an accessory to the Time Traveler's murder of her enemy's ancestor.
Made all three characters smell like a dinosaur at once.
Stood by and watched as the Twins murdered their parents.
Watched Mummy and Daddy's furniture get broken all to bits.
Came ever-so-close to recovering the Sarcophagus.
Pantomimed an ancient hieroglyph.
All three characters killed by one Miner's dynamite.
Saw a postcard stolen from the Gift Shop.
Witnessed a hot dog cooked with the monster's breath.
Reached the bottom of The Cave.
Shared in the blame for the Scientist's act of mass murder.
Enabled the Hillbilly to burn down the Carnival.
Helped the Knight obtain Excalibur.
Nobody died.
Saw the good in everyone.
Collector of forgotten dreams.
Where did the King go anyway?
The scale reveals a baleful figure.
Broke bridges.
Peered into everyone's fate.