The pitch-black "Bota-yama Curry" from Fukuoka is inspired by the image of Bota (discarded stones from coal mining) mountain in a coal mine. A specialty of the Iizuka Garrison of the Japan Ground Self-Defense Force.
I tried "Bota Mountain Curry," a specialty of the cafeteria at the Iizuka Camp of the Japan Ground Self-Defense Force in Fukuoka. The curry is made with spices to resemble "coal black" and is filled with diced beef.
