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)
Collect all the Red Bricks. (Single Player Only)
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)
Dress a character completely in treasure items.
Craft the Fire and Ice Bows. (Single Player Only)
Use the Ent Draught on Pippin.
Travel to Isengard as every playable Hobbit.
Turn an enemy into a skeleton and make them dance.
Equip Aragorn with the Mushroom Crown.
Travel to Trollshaws as Bilbo.
Complete 2 cooking puzzles.
Complete the Bonus Level.
Defeat Gollum as Gollum.
Achieve True Adventurer in every level. (Single Player Only)
Complete 'The Black Gate'.
Complete 'Mount Doom'.
Unlock all the Map Stones in Middle-earth. (Single Player Only)
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'.
Defeat 42 Uruk-hai as Legolas.
Finish one of Gimli's opponents as Legolas in 'Helm's Deep'.
Complete 'Warg Attack'.
Complete 'Track Hobbits'.
Complete 'The Dead Marshes'.
Complete 'Taming Gollum'.
Fish perfectly 20 times by pressing the icon as it flashes.
Complete 'Amon Hen'.
Reach the top of Amon Hen without being caught once by Boromir. (Single Player Only)
Complete 'The Mines of Moria' in under 15 minutes.
Complete 'The Mines of Moria'.
Complete 'The Pass of Caradhras'.
Throw Gimli 30 times.
Form The Fellowship of the Ring.
Complete 'Weathertop'.
Complete 'The Black Rider'.
Complete a level in co-op.
Complete 'Prologue'.
During 'Prologue', jump into the fires of Mount Doom as Isildur.