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.
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)
Collect more than 10,000,000,000 studs. (Single Player Only)
Travel to Isengard as every playable Hobbit.
Collect all the Red Bricks. (Single Player Only)
Dress a character completely in treasure items.
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)
Turn an enemy into a skeleton and make them dance.
Complete 'The Mines of Moria' in under 15 minutes.
Achieve True Adventurer in every level. (Single Player Only)
Defeat 42 Uruk-hai as Legolas.
Fish perfectly 20 times by pressing the icon as it flashes.
During 'Prologue', jump into the fires of Mount Doom as Isildur.
Complete the Bonus Level.
Travel to Trollshaws as Bilbo.
Complete 'Mount Doom'.
Complete 'The Black Gate'.
Complete 'The Battle of Pelennor Fields'.
Defeat an Oliphaunt as Legolas.
Unlock all the Map Stones in Middle-earth. (Single Player Only)
Walk into Mordor.
Complete 'Cirith Ungol'.
Complete 'The Secret Stairs'.
Throw Gimli 30 times.
Defeat Gollum as Gollum.
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 2 cooking puzzles.
Complete 'The Dead Marshes'.
Complete a level in co-op.
Equip Aragorn with the Mushroom Crown.
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'.