Very beautifully written and very immersive.
I loved to get to know these women and their relationship, especially through Miris eyes. All these little details she thinks of while trying to find her Leah in the Leah that returned. It was hurtful to read, but also endearing. (My favourite was when Miri said that Leah used to pedal Miris legs when she was upset and chant "tour de france, tour de france" until Miri had to laugh. Idk, it was just so cute.) Miris voice was very clear, every obersvation and comment she made fit her perfectly. Same for Leah, but we don't get to see that much of her compared to Miri. 
I liked how the book was seperated into the different stages of the ocean and everything Leah told us about it and the ways to travel and research it. Her fascination for the ocean is everywhere and as someone who is a little fascinated by the deep as well, I liked that a lot.

Even though there's not that much happening, a lot of suspense builds up over the course of the novel. I couldn't put it down after a certain point. - And I get why we don't get all the answers, this book isn't about the plot, and I think it was the right choice, because solving every mystery would've taken away from the point ... but I can't help but want to know the answers. Someone please rewrite this in another genre? So we got both?