In Fable 3 for the Xbox 360, you can open the Millfields Demon Door by being extremly unattractive.
To pull this off, you’ll need to be fat and dress awful as well. To check your weight, look at your Hero Status in the Sanctuary. You’ll want this meter to go all the way to the right. Do this by eating lots and lots of food and booze until the meter is maxed out.
In order to be awfully dressed, the easiest method is to wear your pajamas and color them mismatching colors in the Sanctuary. Try to wear ugly facial hair, and tattoos as well.
Once you’re fat and ugly, the door will let you in where you’ll find 40 guild seals.
If you’re having troubles getting it to open, try sleeping in a house nearby after you’ve made your changes. Some people have reported that this may help the door recognize all of the changes you’ve made.