Demon doors can be found around Albion, they gaurd ancient relics and items. To open them you have to prove yourself by either solving their riddles, accomplishing tasks or simply wearing the right equipment.
Lets go to the demon door in the guild grounds. If you don't remember how to get there, go from the map room, along the red carpet into the dinning hall, up the stairs on the right, turn right and cross the bridge, go right and follow the edge until you get to the next bridge, cross it and keep going straight over the rocks.
Quite simple to figure out, but if you need the answer, simply find your lamp in Items - Others, use it in front of the demon door.
Inside there is a chest, a table with a book on it and two book shelves.
Go to the lowest point on the mini-map for Greatwood Gorge, near the exit is a demon door. It requires you to be evil, but you can counter the EVIL points the same way you earn them for the door, with food. Plus, inside you can find the first Legendary Weapon, so it is recommended.
You need to obtain 50 evil points in front of the door. One way to achieve this is to get 12 Chruchy Chicks.
Right now the only way you can buy them is from wandering traders, just keep going back and forth between Greatwood Entrance and Greatwood Lake, eventually a trader will have them.
Come back to the door with 12, eat them one at a time. This is were a lot of people screw up by just throwing the Chrucky Chicken onto a quick button and eating it all in 2 seconds. That does not work! You need to eat them slowly. There is about a 1-2 second delay after the evil points are given before you will get more evil points for eating another.
So, make sure you are standing in front of the door, eat one, wait, eat another, wait, eat another, etc. Try after 10, if he won't open, eat the last ones and try again. 12 is slightly more than you need but useful if you do eat one too soon and don't get the evil points. You only have to gain 50 evil points in front of him to open up, and if you mess up with just 10, you would have to do it all over again, so the extra 2 may save you a trip back to the traders.
Now, if you are trying to be a pure GOOD character, just buy 12 Tofu and eat them the same way after, it will be as if you never earned the EVIL points to get in.
Note that the door will also open if you're just plain evil already. It will not open if you just have skin-coloured horns, but it will open when you are nearly at full demon horns, so the required level of evil is somewhere inbetween.
There are a bunch of vines inside this place, as well as a chest.
Inside the chest you will find:
When you enter the Darkwood Marshes, you can find this door on the left.
"If you request, my Guardians will test your mettle in combat. Meet their challenge, and the reward I hide is yours."
This can be either easy, very easy, or very hard. If you are doing this during Trader Escort you will not only have to fight a small army of Hobbes, but you will still have to protect the traders you are escorting because they believe they can fight these Hobbes. If you don't want to do it yet, come back later and do it then.
Now, when you say yes, there will be 5 waves of Hobbes, each wave is harder than the last.
Because you are able to have the "Wellow's Pickhammer" by this point and because it is about the strongest weapon you can get for now, it has been used to calculate the required hits:
Inside you find a chest.
From the main path coming from Darkwood Weir, take that first left at the first tree on the left, you will find the demon door behind a wall.
Go and buy like 100-150 gold worth of food (or 25-30 pieces of food) and come back to the door. You could go to the trader near the water's edge here at Barrowfields. Make sure your health is full and eat away.
Inside you find a chest.
At Rose Cottage is an impossible to miss demon door on your left when you enter the area.
Give it a gift. You don't need to use an expensive one; a Red Rose or a Box of Chocolates will do just fine.
If you don't happen to have either just go out the exit, usually you can find 4 or more traders here, just keep going back and forth until you find a trader with chocolates.
When you give it a gift, it will let you in where you will find a chest.
There is a Demon Door at the Greatwood Caves.
It says exactly what it wants to see. It wants you to talk to it when you have a high combat multiplier (in this case, 14 or more).
The easiest way to do this is to have physical shield for starters, but that won't give you the high combat multiplier. There are two methods.
The second option is for those not using Physical Shield, but if you have it either way is incredibly easy.
When you talk to the door with a 14 or high combat multiplier on your screen it will open up and you will find a chest.
In the Witchwood Stones area, the demon doors is on the right hand side
when you enter the area, this is a quest required door.
"I only open to those who know my name. If you know it, find and
hit the magic stones to spell it out."
"Only one person knows my name, but I doubt you'll find him.
Even at the Temple of Avo."
The name is "HITS" spell it out on the stones located in the same area.
After the quest you can find these items:
Inside the barrels you will find:
1 x Ruby
1 x Sapphire
1 x Red Meat
Inside the cart you will find in the chest:
1 x Resurrection Phial
Inside the chest you will find:
1 x Chainmail Leggings
On the ground by the bookshelf you will find:
1 x The Sock Method
1 x Creatures of Albion Book I
1 x A Love Story
On the bookshelf you will find:
1 x Howl Tattoo
Before entering the gates into the town on your right is the demon door.
"If you can hurt my face with an arrow, I'll crack wide open
for you."
All right... shot him with an arrow.
I opened him using the Oak Crossbow and level 5 accuracy stats.
I also opened him using the ------------------ and no accuracy stats.
All there is here is a chest.
Inside the chest you will find:
1 x Elixir of Life
Warp to Twinblade's Camp, go out the exit to Abandoned Road, the Demon Door is just off to the right.
Now, you will need to have the full Bright Plate Outfit, the full Dark Will user's Outfit and the full Bandit Outfit to enter this door. If you didn't buy the Bright Plate Outfit from the Arena, you will need to walk around Witchwood talking to wandering traders until you find one with the gloves and chest piece, then go to Knothole Glade and buy the leggings and boots from the shop.
Inside is a single chest.
Inside the chest you will find:
This door doesn't have any secrets or anything, its just to prevent you from leaving before beating Thunder.
Beat Thunder.
At the top right corner of the mini-map you can find this Demon Door.
Well, you need to marry Lady Grey, see [MI] on how to do that, you will need to be at least past the arena to do this.
Inside is a single chest.
Inside the chest you will find:
1 x Ronok the Axe
In the Lychfield Graveyard, this quest-only demon door blocks your path to the prison.
You will need to find Nostro's Sword, Shield, Armour and Helmet.
Give all four items to Nostro's Skeleton to open the door.