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.
Turn an enemy into a skeleton and make them dance.
Craft the Fire and Ice Bows. (Single Player Only)
Dress a character completely in treasure items.
Use the Ent Draught on Pippin.
Equip Aragorn with the Mushroom Crown.
Travel to Isengard as every playable Hobbit.
Defeat Gollum as Gollum.
Fish perfectly 20 times by pressing the icon as it flashes.
Unlock all the Map Stones in Middle-earth. (Single Player Only)
Achieve True Adventurer in every level. (Single Player Only)
During 'Prologue', jump into the fires of Mount Doom as Isildur.
Travel to Trollshaws as Bilbo.
Throw Gimli 30 times.
Complete the Bonus Level.
Reach the top of Amon Hen without being caught once by Boromir. (Single Player Only)
Walk into Mordor.
Complete 'The Mines of Moria' in under 15 minutes.
Complete a level in co-op.
Defeat 42 Uruk-hai as Legolas.
Finish one of Gimli's opponents as Legolas in 'Helm's Deep'.
Complete 'Mount Doom'.
Complete 'The Black Gate'.
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'.
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 2 cooking puzzles.
Complete 'The Black Rider'.
Complete 'Prologue'.
Collect all the Mithril Bricks. (Single Player Only)
Complete all the Fetch Quests in Middle-earth. (Single Player Only)
Get 100%. (Single Player Only)
Collect all the Red Bricks. (Single Player Only)
Craft every Mithril item. (Single Player Only)
Unlock all characters. (Single Player Only)
Collect more than 10,000,000,000 studs. (Single Player Only)