Here is the full list of all 48 LEGO The Lord of the Rings achievements. It takes around 30-35 hours to unlock all of the achievements on Windows.
Complete 'The Mines of Moria' in under 15 minutes.
Complete a level in co-op.
Get 100%. (Single Player Only)
Collect all the Red Bricks. (Single Player Only)
Complete all the Fetch Quests in Middle-earth. (Single Player Only)
Craft every Mithril item. (Single Player Only)
Collect all the Mithril Bricks. (Single Player Only)
Collect more than 10,000,000,000 studs. (Single Player Only)
Achieve True Adventurer in every level. (Single Player Only)
Defeat an Oliphaunt as Legolas.
Travel to Isengard as every playable Hobbit.
Travel to Trollshaws as Bilbo.
Defeat Gollum as Gollum.
Unlock all characters. (Single Player Only)
Craft the Fire and Ice Bows. (Single Player Only)
Defeat 42 Uruk-hai as Legolas.
Turn an enemy into a skeleton and make them dance.
Fish perfectly 20 times by pressing the icon as it flashes.
Use the Ent Draught on Pippin.
During 'Prologue', jump into the fires of Mount Doom as Isildur.
Unlock all the Map Stones in Middle-earth. (Single Player Only)
Complete the Bonus Level.
Throw Gimli 30 times.
Complete 'Mount Doom'.
Reach the top of Amon Hen without being caught once by Boromir. (Single Player Only)
Dress a character completely in treasure items.
Complete 'The Black Gate'.
Walk into Mordor.
Complete 'Cirith Ungol'.
Complete 'The Battle of Pelennor Fields'.
Complete 'The Secret Stairs'.
Complete 'The Paths of the Dead'.
Complete 'Osgiliath'.
Complete 'Helm's Deep'.
Finish one of Gimli's opponents as Legolas in 'Helm's Deep'.
Complete 'Warg Attack'.
Complete 'Track Hobbits'.
Complete 'The Dead Marshes'.
Complete 2 cooking puzzles.
Equip Aragorn with the Mushroom Crown.
Complete 'Taming Gollum'.
Complete 'Amon Hen'.
Complete 'The Mines of Moria'.
Complete 'The Pass of Caradhras'.
Form The Fellowship of the Ring.
Complete 'Weathertop'.
Complete 'The Black Rider'.
Complete 'Prologue'.