Castles that have been Nationally designated as historical landmarks by the Ministry of Education. This is an ever changing category as you sometimes see castles newly registered as National Historic Sites. If a site had been previously designated as a Prefectural Historic Site at the prefecture level and is then named so at the National level, then the prefectural designation is removed. Historical landmarks to be considered for national recognition should be important sites to the understanding of Japanese history and hold sufficient interest for academic and research purposes. While it's not officially part of the process, my understanding from people who have been involved with the process is that there is also much burden on the local municipality to prove that historical significance and they need to make some commitment to protecting and preserving a site for it to gain such recognition.
National Historic Site
National Historic Site# QUERY7fcf2a991d34bea6274d2e988dead0cf
National Historic Site# QUERYe0d4ac611070911fc1f258214a6cbc32
National Historic Site# QUERYcb8c507a8310bd60e8dc6cde0740524d