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