I've thought about this often, but not nearly given it enough thought. And if that sentence trips you up, sorry; I just got out of bed 20 minutes ago.
I can remember, perhaps going back between 10 and 12 years (things get hazy after a while, and some of these might go back further. It's very likely), places I have revisited in dreams but that are not representations of places that I have been to in real life. They're, as far as I'm concerned, true "dreamscapes". Some of these are whole towns, and whenever I find myself in them I can remember, from having been there before, streets, shops, houses, etc.
Of course, I'm fascinated by the potential function behind all of this. What is my subconscious trying to represent to me in these dream realities? What makes it all the more intriguing is that i have found myself thinking of these places when awake, and for moments having my brain process them as real places before realising 'You silly sod - that's not a real place.' At least, not in this reality, right?
Anyone else have similar experiences? I'd love to hear more.