If you're as much a completionist as I am in games, then you'll have a lot of fun with Diablo III—a title that's literally (metaphorically) burdened with more secrets than you can shake your fists at.
Among the secrets you'll have fun uncovering are a host of secret dungeons that only have a small chance of appearing each time you enter certain parts of the game—and every part of the game seems to have a few of these around.
You'll need to visit each and every single one of these secret dungeons and read various books and manuscripts found throughout these areas to acquire the related achievements.
We'll start off with the game's first three acts and their secret and not-so-secret dungeons.
Act 1: No Stone Unturned
To acquire this achievement, you must visit all of the following locations.
- The Cave Under the Well – Old Tristram Road
- Musty/Dank/Damp/Dark Cellars – Old Tristram Road
- Mass Grave – Old Tristram Road
- Den of the Fallen – Weeping Hollow
- Lost Mine – Fields of Misery
- Scavenger's Den – Fields of Misery
- Decaying Crypt – Fields of Misery
- House of Curios – Fields of Misery
- Farmer's Cellar – Fields of Misery
- Tinker's Hovel/Pillaged Home – Fields of Misery
- Cave of the Moon Clan – Southern Highlands
- The Lyceum – Southern Highlands
- Abandoned Servant House – Southern Highlands
- Watch Tower – Northern Highlands
- Highlands Cave – Leoric's Hunting Grounds
Act 2: Nooks and Crannies
Much like Act 2 in the previous game, Act 2 of Diablo III takes place in the desert—this time in the sands surroundings the city of Caldeum. The sands hide a number of secret dungeons that you'll have to revisit multiple times to uncover.
Notably, the Fowl Lair and the Veiled Treasure can only be accessed through a special portal device that spawns very occasionally.
- Hadi's Claim Mine – Stinging Winds
- Abandoned Cellar – Stinging Winds
- Tunnels of the Rockworm – Black Canyon Mines
To access this dungeon, you must kill a unique Rockworm.
- Sirocco Caverns – Howling Plateau
- Chamber of the Lost Idol – Stinging Winds
- Tomb of Khan Dakab – Dahlgur Oasis
Located in the Dahlgur Oasis, the only way to access this dungeon is to activate two levers to open the door.
- Tomb of Sardar – Dahlgur Oasis
Opening this tomb requires that you hit a lever by the entrance.
- Cave of Burrowing Horror – Desolate Sands
Killing a unique Rockworm opens this dungeon.
- Mysterious Cave – Dahlgur Oasis
Located in the south of the map, you must first save a merchant from ghosts.
- The Veiled Treasure – Desolate Sands
Accessible only through the portal device.
- The Forgotten Ruins – Dahlgur Oasis
- The Fowl Lair – Desolate Sands
Accessible only through the portal device. It's even rarer than the Veiled Treasure.
- The Ruins – Stinging Winds
- The Crumbling Vault/Vault Treasure Room – Stinging Winds
- Vile Cavern – Desolate Sands
- Ancient Cave – Dahlgur Oasis
- Flooded Cave – Dahlgur Oasis
- Alcarnus/Sandy/Town Cellars – Alcarnus
- Abandoned Mineworks – Howling Plateau
- Fuad's Cellar – Howling Plateau
- Rotting/Ransaked/Storage/Old Fisherman's/Storm/Swampy Cellars – Dahlgur Oasis
- Deserted Cellar – Black Canyon Mines
Act 3: Oh the Places You'll Go!
Now that you're done with Act 2, it's time to move on to the third and penultimate act in the game, which takes place on the battlefields of Arreat. Most of these locations, like those in the previous acts, can only be found occasionally, so you'll have to revisit this location multiple times (preferably on different characters, so you don't burn yourself out) to visit them all.
- Caverns of Frost – Fields of Slaughter
- Icefall Caves – Fields of Slaughter
- Fortified Buncker – The Arreat Gate
- The Barracks – The Arreat Gate
- Battlefield Stores – The Battlefields
- The Foundry – The Battlefields
- Cryder's Outpost – The Battlefields
- The Forward Barracks – The Battlefields
- The Underbridge – Rakkis Crossing
