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 'The Mines of Moria' in under 15 minutes.
Travel to Isengard as every playable Hobbit.
Defeat 42 Uruk-hai as Legolas.
Complete all the Fetch Quests in Middle-earth. (Single Player Only)
Turn an enemy into a skeleton and make them dance.
Defeat Gollum as Gollum.
Use the Ent Draught on Pippin.
Get 100%. (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)
Travel to Trollshaws as Bilbo.
Defeat an Oliphaunt as Legolas.
Craft the Fire and Ice Bows. (Single Player Only)
Unlock all characters. (Single Player Only)
Fish perfectly 20 times by pressing the icon as it flashes.
Walk into Mordor.
Unlock all the Map Stones in Middle-earth. (Single Player Only)
During 'Prologue', jump into the fires of Mount Doom as Isildur.
Equip Aragorn with the Mushroom Crown.
Dress a character completely in treasure items.
Throw Gimli 30 times.
Complete the Bonus Level.
Complete 2 cooking puzzles.
Achieve True Adventurer in every level. (Single Player Only)
Complete 'Mount Doom'.
Complete 'The Black Gate'.
Complete 'Cirith Ungol'.
Complete 'The Secret Stairs'.
Complete 'The Battle of Pelennor Fields'.
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 'Taming Gollum'.
Complete 'Amon Hen'.
Complete a level in co-op.
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'.