The reverse door.
In my dream, I was six years old, and in my house, except everything was reversed, as if I was looking through a mirror.
As I was running about enjoying myself, I decided to go exploring. I walked into a tiny closet in our hall, and found a door.
I opened the door, and walked into a mirror image of my house, except it was empty. Then, in the new house, I went back to the door, and found a secret passage way, which lead to a bunch of new rooms, like a kitchen and a bedroom, that I subconsciously knew was mine.
As I walked around, the room got dark, and I disappeared. Then a buch of toys fell through my room. Then everything went black, and I woke up. I remember I had dreams about this door and the reverse house when I was 6, 10, 13, and 14 years old. Each had the door, and the reversed house was present in all of the dreams except for the one from when I was 14, and all of the dreams were different in all other aspects.
The one I have described here is from when I was 10. I remember the dream from when I was 13 most vividly, but it is very very hard to explain.
I have a really good memory for things, and can remember multiple dreams I had when I was only two!