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