William Kumamoto Castle is known as "Ginkgo Castle" (銀杏城, ginnanjō) due to its large number ginkgo trees, which has become a symbol not just of the castle but of the city itself. Now is the season when they turn a stunning golden-yellow. Another good place to view ginkgo is the entrance to Prefectural Hall.

William Kumamoto Castle is known as "Ginkgo Castle" (銀杏城, ginnanjō) due to its large number ginkgo trees, which has become a symbol not just of the castle but of the city itself. Now is the season when they turn a stunning golden-yellow. Another good place to view ginkgo is the entrance to Prefectural Hall.
Katō Kiyomasa apparently planted the trees inside the castle to provide food for horses and firewood in case of siege.
Legend has it that one immense tree in front of the main keep (tenshukaku, 天守閣) was planted by Katō himself, and that he prophesied, "When the tree's height reaches that of the tenshukaku, there will be an uprising in the castle." Apparently, the height of the tree had indeed reached about that of the tenshukaku by 1878, when most of the castle was burned to the ground in the Seinan War.
The tree was badly damaged during the war, but has regrown to a respectable height.
Info about the relationship between Kumamoto Castle and the gingko trees can be found here (Japanese): http://castle.link-hp.net/22.html and a link to an excellent castle guide: https://castle.kumamoto-guide.jp/en/ (English). A photo of the famous gingko in the autumn is below. Prepare your cameras.