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