Sakurai Futamigaura was high on our must-see list for Fukuoka - I mean, how often do you get to see a white torii gate standing right in the ocean? Add in these "married" rocks connected by one of those massive sacred Shinto ropes (shimenawa), and it sounds like one of those perfectly Japanese photo ops.
The whole setup seems almost too picturesque to be real: white torii gate in the sea, sacred rocks tied together like a geological wedding ceremony, and apparently some of the best sunsets in the area. There's even a sea cave nearby called Keya no Oto that you can explore.
For anyone with more time in Fukuoka than we had: this sounds like one of those spots that makes you understand why Japanese people are so good at finding the perfect balance between natural beauty and spiritual significance. Definitely one for the "next time" list - just try to time it for sunset if you can!