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