During Japan's Sengoku "Warring States" era (1467-1615), castles were constructed, bolstered and fortified all across the Japanese archipelago, resulting in approximately 5,000 individual keeps.
No ranking, not much background info, just a run-down of the usual touristy stuff, mixing up renovated and replica castles with the few original castles still extant.
I have always been reluctant to produce articles à la "The Ten Best [whatever] in Japan" but I guess this is what people want to read nowadays. Meanwhile, our article series on lesser-known Japanese castles has grown to a considerable size, not at least due to the efforts and contributions of @Hiroto Uehara san.