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