The UK would meet your brief perfectly. Not only do we have over 450 official castles ranging from early earthworks to palaces, they range from disrepair to very well maintained. Some are huge with grounds, some small with views. Either way, I am sure that we can find what you need.
Regarding the weather, it is most likely that you will find suitable weather in the UK’s May for Autumn, perhaps more likely here than most places in continental Europe like Spain, France, Italy and Germany which will be much more summery.
Bearing these 2x key factors in mind, I would be heading to the UK. We can facilitate your requirements from scouting to full production and have a great deal of experience of working for German productions.
Please get in touch if you would like to discuss this further.
Luke
+447768524778
http://www.locateproductions.com