Umi Hachimangu is located a little to the east of Fukuoka City. Like all Hachimangu, it enshrines primarily Ojin, the posthumous name of the "emperor" Homuda Wake.
What is unique about this Hachimangu is that it is built on the site where, according to the ancient myths, Homuda Wake was born, and the place name was changed to Umi, derived from the Japanese word for birth.
Along with Ojin, his mother Jingu is enshrined. Often Hachimangu will have Ojins father Chuai and Ojins wife Himegami enshrined, but here it is Tamayorihime, who is sometimes considered to be an individual, and sometimes considered to be a generic word for Miko.
While I was there a ceremony was going on. It may have been a Purification ceremony, but I suspect it more likely to be a ceremony to pray for safe childbirth, something this shrine is particularly known for.