Go to the beach! by schwein
In the area under Fukuoka tower is a beautiful sandy beach, great for swimming!There are restaurants and shops there, so no need to bring food/drinks.
If you're up for it, you can pedal from downtown to there in about 20 minutes. Once you get to the general area, you can ride along the sea-wall/pathway.
For lazy fatbodies, you can take a bus to Fukuoka tower and walk to the beach from there.