In Japanese mythology there is a legend about an island where only women lived. I made it the home of Ryujin, a dragon who is a god of the sea, tossed in the story about a couple of Tide Jewels, and made it the mysterious place I dove on when I was scuba diving in Japan.
The location first appears Leilani’s Illusion: Karov, the sixth book in my Vampires & Strygoi Witches series. It will also be featured in the spinoff series about Karov’s brothers.
The underwater site is a bit controversial in that there is some debate over whether it is manmade or not. It seemed like there were an awful lot of very straight edges to be natural to me.