Here is the full list of all 66 Torchlight achievements. It takes around 100-120 hours to unlock all of the achievements on Windows.
Achieved enlightenment by speaking with the horse 100 times
Retire over 300 levels worth of characters
Complete 50 Hatch Quests
Beat the game with all three classes
Defeat Ordrak on Very Hard Hardcore
Kill 25 champion trolls
Drink 5,000 potions
Defeat Ordrak on Hard Hardcore
Sell 10,000 items to vendors
Die 500 times
Retire two characters
Defeat Ordrak on Normal Hardcore
Retire a character
Defeat Ordrak on Easy Hardcore
Kill 50,000 monsters
Reach level 100
Smash 1500 Breakables
Achieve player level 100
Reach the 50th floor of a dungeon
Achieve maximum fame
Catch 1000 fish
Successfully create 25 items using the transmuter
Complete 200 Quests
Achieve player level 65
Complete 25 Gar Quests
Do at least 10,000 damage to an enemy in a single strike
Gamble 100 times
Successfully enchant one item 10 times
Suffer 20 disenchants from the enchanter
Defeat Ordrak with no deaths
Defeat Ordrak in 8 hours or less
Defeat Ordrak in less than 5 hours
Defeat Ordrak on Easy or Normal
Defeat Ordrak on Hard
Defeat Ordrak on Very Hard
Defeat Alric
Gamble 50 times
Gamble 20 times
Defeat Medea
Collect 250,000 gold
Use 50 potions on your pet
Have 100,000 gold in your inventory
Catch 100 fish
Kill 5000 Monsters
Have an item disenchanted on the first enchantment attempt
10 mods used at the same time
5 mods installed at the same time
Defeat Krag
Gamble a unique item
Permanently transform your pet
Transform your pet into a Mimic
Take 25,000 steps
Successfully enchant one item 5 times
Defeat the Ember Colossus
Catch 50 fish
Equip a spell on your pet
Defeat the Root Golem
Pull 100 levers
1 game mod installed
Defeat the Overseer
Send your pet to town
Fill your pet's inventory
Defeat Brink
Blow 25 enemies to pieces with critical strikes
Change your pet by feeding it fish
Find the entrance to the mine