Here is the full list of all 12 FEZ achievements. It takes around 10-12 hours to unlock all of the achievements on Windows.
Find ALL collectibles.
Collect all 32 Golden Cubes and 32 Anti-Cubes.
Find the Skull artifact.
Get to the end.
Reactivate all 5 warp gates.
Break the code.
Find the Counting Cube artifact.
Find the Tome artifact.
Find the Writing Cube artifact.
Find your very first cube shard.
RTRTLTRTRTLTLTLT
Find an Anti-Cube.