This guide is a WORK IN PROGRESS
Thanks to all the people who have contributed to it and to who will do it in future! :)

O: where you find the object
U: where you can use it

Another guide that could help you into obtaining achievements: http://gtm.steamproxy.vip/sharedfiles/filedetails/?id=1174535260

All the potions can be bought from Oriana the Soul Keeper, who is in the small rock building, heading east with respect to the domain of the dead

Potion of Skill
U: recover skill points
O: in the magic shool section, go west at the first choice, and defeat the enemies. Requires Keen Eye.

Potion of Strength
U: recover stamina
O1: in the dwarven hall, with keen eye
O2: in the river part, arriving from the school of magic, cross the river with stepping stones, look into the hole nearby the dead dwarf to find another chest with the potion inside
O3: founded in the graveyard (pass a luck test) at the beginning of the domain of the dead

Potion of Fortune
O1: In the spiders' cave, in the room with the hole, having a Keen Eyed character
O2: In the school of magic, after che mouth gate, head west, kill the troll and search in the little cave
O3: In the school of magic, in the potion room, upper shelf.
U: recover luck

Potion of Invisibility
O: In the Orcs part, climb the stairs of the room where you find the Dragonfire Spell, get rid of the enemies and open the box (beware of the trap!)
O2: dropped by Ian the White (the scared scholar who is running away from the school of magic) if he is threatened (maybe the trait FEARSOME is needed)
O3: In the alchemy lab of the magic school, mix air, fire and water vial
U1: in the giant's cave in the second part of the dungeon
U2: in the shack near the river, to get the Boathouse Keys
U3: in the boathouse, to avoid skeletons
U4: against the warlock, so it attacks randomly

Potion of Fire Protection
O: In the school of magic, reach the jester room (after the stone stairs, head north) and give him 20 golds
U1: protects from the fire trap in the last part of the dungeon
U2: protects from the dragon's breath in the last part of the dungeon

Lantern
O: starting object for some character
U: before the fight with the warlock, look at his desk and select the cards to set them on fire and weaken the warlock (I've done it only one time, I don't know if it works every time)

Rope
O: starting object for some character
O2: in the school of magic, after the mouth-gate, head west, defeat the troll and explore the little cave

Aardwolf Meat
O: at the first crossroads, head west. Climb the pit and explore the northern cave.
U1: heading east, you'll find two hounds. throw the meat to distract them
U2: in the tower besides the domain of the dead, if you pass a luck test, you can give the meat to the beggar.

Silver Arrow
O: In the room where orc are eating (toward the end, before the cells), walk through the south door
U: Kill the wight in the Domain of the Dead (second floor, right room)

Rune Stone
O: At the end of the orcs part, when you reach a room with four cells, go inside the first one on the left and kill the goblins. Then search the dwarf feet.
U: in the dwarven part of the dungeon, in the room with the stone hands or the crushed goblin, it allow to not get hurted

Cheese
O: At the end of the orcs part, when you reach a room with four cells, go inside the first one on the left and kill the goblins. Then search the goblins
U1: In the school of magic, going left after the wood door, after killing the troll, can be used to distract the giant rats.
U2: in the last fight against the warlock, can be used to make the fight a lot more difficult.

Blue Candle
O: At the end of the orcs part, when you reach a room with four cells, go inside the second on the right and defeat the enemies inside
U: In the dwarven ruins, in the west-most path, in the paintings room.

Bull Amulet
O: Fight the troll in the second room on the west in the second section of the dungeon.
U1: Can be given to the Air Elementalist (school of magic, second door) for the Air Vial
U2: Can be used at the mouth-gate of the school of magic to pass (you'll lose 3 stamina)
U3: Maybe it opens the demon doors in the maze
U4: Allow to pass without harm in the skeleton room before the warlock room, in the last part of the dungeon. (grants an achievement: Domino Effect)

Potion Store Key
O: In the magic school, after the wooden gate, head west. Kill the troll and the rats, than go east. Speak to the woman and accept to help her.
U: Go back to the rats room, and use the key to open the west door.

Earth Vial
O: In the Magic School, defeat the Earth Elementalist (first door)
U: In the Magic School, create a potion in the alchemy lab (after the Water elementalist, keep going west), you must not be illiterate

Air Vial
O: In the Magic School, speak to the Air Elementalist (second door) and give her the Bull Amulet
U: In the Magic School, create a potion in the alchemy lab (after the Water elementalist, keep going west), you must not be illiterate

Fire Vial
O: In the Magic School, defeat the Fire Elementalist (third door)
U: In the Magic School, create a potion in the alchemy lab (after the Water elementalist, keep going west), you must not be illiterate

Water Vial
O: In the Magic School, talk to the Water Elementalist (after the hands and stars room, head west and enter into the first door)
U: In the Magic School, create a potion in the alchemy lab (after the Water elementalist, keep going west), you must not be illiterate

Eye of the Cyclops
O: In the dwarven part of the dungeon, head always west
U1: In the paintings room of the dwarven ruins with the mad man, can be used to defeat the gaze of the warlock
U2: In the fight with the warlock, can be used to kill him instantly

Chalice
O: In the dwarven part of the dungeon, in the west-most path, in the hall after the king statue, a skeleton holds a chalice in his hands.
U: Can be used in the Domain of the Dead to take blood from the pool and, later, to make an offer to the Death statue, to avoid Bloodwing fight

Crucifex
O1: In the dwarven part of the dungeon, in the est-most path, there is a shrine with a crucifex upon it.
O2: In the dwarven part of the dungeon, in the west-most path, in the hall after the king statue, there is one crucifex over a table
U: can be used in the Domain of the Dead to weaken the vampire, if it is approached quietly.

Fire Gem
O: In the dwarven part of the dungeon, in the west-most path, after the skeletons go down the stairs and defeat the enemies
U: Can be used to flee from the cavemen just out of the dwarven dungeon.

Iron Helmet
O: In the dwarven part of the dungeon, in the west-most path, after the skeletons head north and then east.

Bronze Helmet
O: In the dwarven part of the dungeon, in the west-most path, after the skeletons head north and then east.

Gleaming Sword
O: If your character uses a sword, in the river part of the dungeon that is reachable from the west-path of the dwarven ruins, it requires to throw away the previous sword
U: Grants +1 skill permanently

Y-shaped stick
O1: Reaching the river from the dwaven ruins, in the room with two sticks and a rope, take the sticks.
O2: in the vampire coffin, domain of the dead

Boathouse Keys
O: In the shack near the river, after fighting or using Potion of Invisibility
U: open the door of the structure near the pier on the river

Stake and Mallet
O: In the boathouse. Must examine the tools of the skeletons
U: kill the vampire in the domain of the dead (central room, third floor) if you are lucky enough to approch it while it's sleeping

Blood Curse
O: In the domain of the dead, drink from the blood pool in the central room on the second floor (grants an achievement: AB Positively Refreshing)
U: Before the fight with Bloodwing (domain of the dead, fourth floor, left room) you'll lose 1 skill point (inevitable). If you survive, you'll lose the curse and recover 2 skill points.

Shining Jewe
O: defeat Bloodwing (maybe requires Blood Curse to appear)

Earring
O: defeat the ghouls at the end of the Domain of the Dead, you wake them examing the second or the third corpse

Winch Handle
O: in the maze, find a room with a dead ogre and an ork, offer money to the ork (amybe works also if you kill him?)
U: use it in the room with the caged goblin to lower him down.

Crystal (Minotaur/Goblin)
O: in the maze, after killing the respective creature. For the goblin, it is necessary to use the Winch Handle first.
U: use it in the starting room of the maze to go to the second level (when you have both!)

Skull (? dots)
O: the first one by the master of the second level of the maze. The others are founded in the room behind the demon doors. It is also possible to trade the current skull with the fool for another skull
U: open the demon doors

The 400 scroll
O: behind one of the demon doors in the second level of the maze
U: giving it to the master of the maze you'll exit and reach the last part of the dungeon

U: used to open the final chest. The more the keys (max 3) the more the reward (3=150 souls, 2=100 souls)
O: Their position is random.
Some of the possible positions:

• First part: the slime beast room (turn right at the first choice and explore the southern cave)
  
• First part: snake trap room, after killing the snakes
  
• First part: In the orc kitchen, after defeating the cook
  
• First part: in the prison, in the second left door (the shield one)
  
• Second part: kill the ogre in the first cavern on the west or loot him being invisible
  
• Second part: in the room after the ogre, kill the troll
  
• Dwarven ruins: inside the cyclop, eastern most part
  
• Magic school: jester room, in the traps room
  
• River: Oriana may have one, if you ask her about the treasure
  
• River: in the boathouse, inside the drawers
  
• Domain of the Dead: the chest in the Wight room
  
• Domain of the Dead: after the vampire, take the stairs down, light the candle and kill the demon
  
• Maze1: Kill the minotaur
  
• End: dragon's cave
  
• End: Zagor's room