When I was very young my family would often vacataion with another family into the Cascade Mountains. (Oregon, USA)
They would joint-rent a cabin and we would do activities such as skiing, hiking, etc.
The other family had children of the same age as my sister and I and I was good friends with the oldest daughter because we were the same age. When we were in Jr High, about 13, we were reminiscing about our family vacations when we were younger, and had the same memory of going to a cabin that had alcove beds... the kind behind doors that are in the wall. I remember them distinctly because they reminded me of the beds in the Gnome Book. She remembered them as well. There was also no running water in this cabin and you used a hand pump to fill the sink, which was amazing for children of the 80's. We both remembered other small details and experiences about this same trip. A major detail is the two of us locking ourselves outside, alone, and how scared we were, and how relieved we were when our parents opened the door. We were probably 6 or 7 years old when we went to that cabin.
We asked our parents about this cabin and told them what fun we had when we went there, because they were planning another vacation and asked us where we wanted to go (the beach or the mountains) and we told them we wanted to go back to that cabin again. None of them remembered the cabin, even after we described details such as the bed and the hand pump. They said we never stayed in a cabin that had a hand pump or one with alcove beds, and it doesnt seem as though we're combining memories of multiple trips into one "imagination cabin" either.
None of them remember us locking ourselves outside either.. however that can be explained as an easily forgettable experience on an adults part since what is minutes to a grown-up can be an eternity for a child.
I'd still like to go back to that cabin, and Sarah and I both still recall it vividly.