This is a lovely castle and museum. Enjoy the climb to the top as there are many steps. It is worth it.
There aren't many well-preserved historical Japanese castles on the island of Kyushu, but Kumamoto has a good one. After you've toured the castle, head over to Suizen-ji garden, one of the most famous traditional gardens in the country. (No kidding, it's a national landmark - but why is it so far out of the way down in Kyushu? Good question.)
Kumamoto castle was designed by lord kiyomasa kato.
You will want to clime up the stone base of Tenshu.
Beautiful painted doors