Forgotten Keep

Location: Bowerstone Cemetery
How to open: This Demon Door is hungry and wants to eat some meat.
You can buy him anything or you can kick a chicken towards him. He will open his mouth wide, and you will get some experience points.
Reward: Balverine Strength potion, Practiced Skill potion, and Infused Will potion

Homestead

Location: Oakfield
How to open: This Demon Door wants to see true love. Have a person fall in love with you, then make them follow you. Propose to him or her in front of the door, and he will open. If you are already married, have your spouse follow you to the door. After the door speaks to you, blow him or her a kiss, and the door will open.
Reward: Serenity Farm marital home, "Come Hither Dear" book (teaches the expression "Come Back To My Place"), and the legendary mace Hammerthyst

Memory Lane

Location: Rookridge
How to open: This Demon Door wants to see a dog show. Have your dog perform four different tricks. Perform an expression, and depending on what your dog knows, he will react to it. For example, Point and Laugh, and the dog will urinate on the door; Fart, and the dog will cower; play fetch and do the Chicken expression, and he will roll over.
Reward: Potion Of Life

Terry Cotter's Army

Location: Wraithmarsh
How to open: Bring a large audience to him. You need at least ten followers. Note: Have people follow you, then fast travel to "The Drowned Farm". Sometimes a Banshee will be here. If so, use Time Magic to slow down their minions, and kill them quickly before you lose your people.

The Arid Sea

Location: Bower Lake
How to open: Respond to his script using expressions. To perform all the required acts, you must progress through the game, and spend some time in the bookstore buying and learning expressions. Many of those can be learned in books from the Bowerstone Book Store, but several (for example, Laugh and Worship) can only be acquired based on your actions and renown. The order is Laugh, Fart, Point and Laugh, Middle Finger, Vulgar Thrust, Growl, Bloodlust Roar, Worship, Dance, and Blow A Kiss.
Reward: Lucky Charm Augment

The Sanctum

Location: Fairfax Gardens under the castle
How to open: Will not open until he is the last Demon Door remaining.
Reward: Marcus' Poems and 50,000 gold

The Sepulchre

Location: Brightwood
How to open: You must have cheese to open the door. After that, he will tell you to get Muttonchops (also known as The Chops) from the Bowerstone barber and a Posh Gentlemen's Shirt or Noble Blouse from the Bowerstone tailor. When you have those, go to Oakfield, and buy the Farmer's Hat from the clothing stall. Next, go to Bloodstone, and buy the Dreadlocks from the barber. Finally, buy the Strumpet Skirt from some of the wandering traders (can be found around Rookridge). The main objective is to get your Ugliness as high as possible.
Reward: Merchant's Cap, Knotted Shirt, and Harlequin Trousers

The Vault

Location: Westcliff
How to open: This Demon Door wants to see someone very bad. You must have a Corruption level that is higher than the Purity level. The easiest way to do this is buy real estate, and drive up rents and prices on your properties. You can check your Corruption level by pausing the game, selecting "Logbook", and viewing your Personality.
Reward: The legendary mace, Calavera

Winter Lodge

Location: The path leading from Wraithmarsh to Bloodstone.
How to open: Play a lute perfectly. This takes a while as you must hold the expression.
Reward: Master Longsword