Fukuoka Prefecture is located on the island of Kyūshū at the northen tip of the island with the closest distance to main island Honshu across the Kanmon Straits. 18% of the land area of the prefecture is designated as natural parks . Nevertheless, the main cities form one of Japan's main industrial centers, accounting for nearly 40% of the economy of Kyūshū.
Right south of the city Kitakyushu is a forested mountain ridge, which is composed of limestone and karstified. It is known as カルスト高原 平尾台 (Karst plateau Hiraodai), named after the village Hiraodai. It is only 6 km long and 2 km wide. Here numerous caves are known, and four of them are show caves open to the public. So many caves all at the same location works only if there are quite a lot of tourists and if every cave has a specialty. You can find a huge entrance pit and a cave where you wade in the cave river.
Not only the limestone is of interest here. There is also coal to be found in the sedimentary rocks. As Japan is a country with few resources, coal mining was of great importance, but eventually it became cheaper to buy on the world market. As a result the coal mining collapsed and the collieries were closed. The town Tagawa City has numerous coal mining related sights.