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