Here is the full list of all 55 Ancient Dungeon achievements.
Discover (almost) all items.
Complete the delve of every Sealed Soul.
Damage The Beast with the Mercenary's Armament in hard mode.
Damage The Beast with the Assassin's Armament in Hard Mode
Escape the dungeon without obtaining any upgrade items.
Fully augment the Assassin's Armament.
Complete 3 unique sealed soul delves
Raise your merchant discount to 60%.
Eat every type of food item during a single delve.
Escape the Ancient Dungeon in under twenty minutes.
Win big on The Merchant's slot machine.
Escape The Ancient Dungeon after re-entering three times.
Fully augment the Mercenary's Armament.
Escape The Ancient Dungeon without consuming any food items.
Traverse The Luminous Mines without taking any damage.
Escape The Ancient Dungeon after re-entering twice.
Traverse The Beast's Cradle without taking any damage.
Throw a dragonfruit into a pit.
Use a Bandit Box at least twenty times during a single delve.
Escape the Ancient Dungeon without entering a shop.
Carry more than two hundred fifty coins during a single delve.
Traverse The Forgotten Library without taking any damage.
Escape The Ancient Dungeon after re-entering once.
Traverse The Overgrown Gatehouse without taking any damage.
Use a Contracting Orb to shrink yourself.
Defeat a Golden Slime.
Consume a food item made of gold.
Acquire four items from shops during a single delve.
Acquire more than five full hearts of health.
Carry more than twenty keys during a single delve.
Damage The Beast with the Mercenary's Armament.
Traverse The Infested Dungeon without taking any damage.
Use The Blacksmith's Anvil to augment a weapon.
Damage The Beast with the Assassin's Armament.
Damage The Beast for the first time.
Defeat one hundred aberrant enemies.
Destroy one thousand pots.
Defeat a boss enemy with a single strike.
Strike enemies with a ranged weapon twenty-five times in a row without missing.
Destroy a Sacrifice Statue.
Explore two hundred fifty rooms within The Ancient Dungeon.
Discover a secret room in the ceiling.
Deal at least twenty-five damage with a single strike.
Defeat a Possessed Armor.
Defeat a Mad Merchant.
Defeat a Chest Mimic.
Acquire three highly powerful items during a single delve.
Lower your merchant discount to -100%.
Discover a secret room in the wall.
Overcome a Challenge Chest's trial.
Enter The Ancient Dungeon for the first time.
Challenge and destroy a boss with only a half-heart of health
Open 250 chests
Escape The Ancient Dungeon with a difficulty modifier of 2.25
Escape The Ancient Dungeon with a difficulty modifier of 3.00