Ray is very secretive about his ideas - why not, the times that the Kinks have been ripped off, especially in the early years, it makes you a little bit cautious about telling anybody what you're doing. And that's understandable.
It was relatively easy to write 'The Cave of Lost Souls', though, because it came to me one night in a dream. I remember waking up and having this idea for a complete story - from start to finish - in my head, so I jotted it down, then later began writing the thing.