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