Oh wow, how amazing you are! I searched on 'base', 'baseplate', 'base plate' and 'floor', and still couldn't find it.
It looked quite new, so I couldn't imagine that I'd received it in a secondhand mixed lot, but I simply had no other idea about where it came from.
Of course .... Mr Raven bought that set some long time ago. We'd planned an afternoon out, and then decided that the money we spent on the afternoon out would be gone as soon as the afternoon had ended. But if we spent the same amount of money on Playmobil, we'd have it forever. And so we went to the toyshop, and he bought that Unicorn Jewel Castle.
We've used parts of it in various things but never that baseplate again.
It has been bothering me for some time; I have a container marked 'Grey Baseplates' - all the usual squares and rectangles ... and that one. Looking at me. In an 'I am lovely, but you have no idea what I was used for' sort of way.
Many thanks.