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