We have introduced Fukuoka Castle before, but as you know it is just a ruin nowadays. The closest intact castle to visit from Fukuoka is the Kokura Castle in Kitakyūshū. The city does offer a lot more than just the castle though.
The city of Kitakyūshū (北九州), located in the North of Fukuoka Prefecture, has a history of being an industrial node in Japan producing steel for the whole country. This resulted in a bad reputation for the city regarding dirt and air pollution. While that might have been true in the 60’s, nowadays Kitakyūshū is one of the most advanced Japanese cities in regards to the protection of nature and recycling.
Kitakyūshū is a merger of the towns Kokura, Tobata, Moji, Yahata and Wakamatsu. The old town names are still used as the city district names.