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