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