This is the extreme conclusion of Bigger on the Inside. Rather than being an item with interior dimensions fitting for the shape but larger, there is nothing but a lonely door to be seen on the outside. Of course, this door or portal does lead somewhere, somehow.
When a character opens the door and crosses it, he ends up in a room, or even an entire palace, that should have been seen from the outside. Sometimes, there is a building there, but it's invisible and the door is the only thing you can see. More often, it is a Portal Door leading to some other dimension or magical realm. In the latter case, expect the character to examine the door by walking all the way around it.
- The Lonely Door is a very common subject of surrealistic artworks, often used in photography (you can find examples here and there and a lot of others there). Often, the door is left closed, and the artist expect the viewer to know that they are very likely to go somewhere else than behind the door if they open it
- In the Donald Duck story Donald Duck's fantastic invention, by Michel Piédoue and Claude Marin, strange aliens are hiding in a lab that can only be entered through a large stone door standing in the middle of a very small island (too small, actually, for the lab to be actually located there). Donald Lampshades this by saying once he is in the laboratory after having been through the door that "he'd have sworn that there was nothing behind the door". This is never explained, though: it is just a small example of these aliens's weirdness among a bunch of other details.
- In Supergirl story arc Bizarrogirl, super-villain Dollmaker abducts a child using a door which appears and disappears on a brick wall.
- The doors used by monsters to enter kids' bedrooms in Monsters, Inc.. These doors are each twinned with a specific location in the human world, but they need to be hooked up to special mechanisms to "work" as Portal Doors, otherwise they're just mundane pieces of wood. There is also a door used to banish people to the tundra.
- In Disney's take on Alice in Wonderland, when Alice is about to wake up from her dream, she comes across the door she previously met in the Rabbit's Hole. As the entire Wonderland realm has faded away, all that's left is the door floating in space. When Alice looks through the keyhole, she sees that the real world is on the other side, but it's obvious that there is nothing behind the door, not even a wall.
- The Chronicles of the Imaginarium Geographica: The adventure in The Indigo Dragon starts when John, Jack and their friend Hugo discover one while walking in the woods near Oxford, and then Hugo goes through and disappears when the connection ends.
- The Chronicles of Narnia: The Last Battle: the doorway to the stable exists standing by itself in Aslan's Country. Unusually for this trope, the door is freestanding in the "inside" world, rather than the "outside" one (where it's a part of the aforementioned stable).
- In Dirk Gently's Holistic Detective Agency, there's a time machine that manifests itself by creating a doorway on the nearest convenient wall — or, when we first see it, on a bare rockface. At one point, the characters go back in time to visit the dodo before humans discovered it and made it extinct, and there are no walls, so it's just a door standing by itself in the middle of the forest.
- In The Drawing of the Three, Book II of The Dark Tower, Roland the Gunslinger finds a series of three doors on a beach along the Western Seain Mid-World. Each one leads into the body of someone living in New York City at different time periods. Each are free standing, and invisible when viewed from behind. More such doors are found as the series continues, though they just lead to Earth, without having to possess anyone.
- In Lindsey Stirling's music video for "Take Flight", a single door with lightbulbs hanging in front of it is seen at the end of Lindsey's journey. The door leads back to Lindsey's own house.
- Kingdom of Loathing has The Inexplicable Door which leads to The 8-Bit Realm, parodying the trend in videogames of the 8-bit era to connect levels or areas with a door which is not attached to any building.
- the entire game of Distorted Travesty 3 is built around this concept. With the six major stages of the game (as well as the eight nightmare gates) being called 'gates' being portals of this nature. Somewhat justified as all this takes place inside a computer.
- In King's Quest II, there are three locked doors in the middle of nowhere, one right behind the other. Once you unlock all three, you can walk through to another world.
- King's Quest VII has the Faux Shop, which is just a false store front (the type that gets used in movies); the only way to enter is to take a grain of salt before walking through the door.
- In the Wander over Yonder episode "The Void", Wander and Sylvia encounter a doorknob floating in space. When Wander turns it, it opens a door into the White Void Room alluded to in the title. At the end of the episode, they encounter a large floating window.
- A one-off gag from My Little Pony: Friendship Is Magic, in which the door is slammed to end a conversation even though there's no wall around it.
- In Bucky O'Hare and the Toad Wars there is a door like this on the Righteous Indignation: it leads to Willy's dimension.
- Looney Tunes:
- In "Porky in Wackyland", the Do-Do draws a door in mid-air, then enters it by lifting it up like drapes and going under it. Porky tries to force the door open, even though he could easily go around. Do-Do then peeks from a window floating in mid-air and Porky goes through it. And then we see the door from the other side as an elevator, which then rises up into the sky. Yes, this is a strange cartoon.
- "Operation Rabbit" starts with Wile E. Coyote placing a portable door outside of Bugs Bunny's burrow just so he'll have a door to knock.
- In the Adventure Time episode "What Was Missing", the Door Lord is capable of creating isolated Portal Doors like this, as well as in two-dimensional surfaces.