Hey there is a cat door in the door between my hallway and my laundry room; that works!
I never responded because the thread never struck me as something I could contribute to without piggy-backing or being silly.
BUT, if you insist.... Fae are said to live within a domain separate but overlapping our own (ethereal, 4th dimension, whatever you want to call it). Therefore, they are aware of our boundaries locations but are not bound by them. They can pass through walls, they can change form, they can manifest as they will onto our realm, etc... Physical doors aren't required.
That doesn't mean you won't see doors or passageways that have been created by humans who:
a) have a fondness for the Kindly Ones and like to attract them to their homes by creating doors/gardens/homes for them to make them feel welcome.
or b) have witnessed the Fae on one of their journeys and have seen the path they walk (Faery Lines stay constant) and have placed a tiny passage-way there for them as a sign of respect.
Lore dictates that you should leave a door/window/gate open for Fae during the nights they travel; because if you don't they will get lost and stranded within our world (much like humans can become stranded in theirs). And that attracts no end of ill-will toward yourself.
Are you happy now?
I need coffee...