I know there are a few castle maps. But they all only have one castle on them.(This is not including the Feudal or AoR maps) My suggestion is a map with more than one castle on it. Sorta like a huge battle ground with more than castles and mabye a couple of forts. Sorta like this map, just something to get an idea of what I mean.
http://sillysoft.net/lux/maps/Castle%20Lux%20HD
Thoughts.