"Percy told me about it," Magnus says. "Annabeth's boyfriend? He's the son of an ocean god. Poseidon, not Ran or Aegir or Njord. So he can withstand it. He was trying to teach me how to not die immediately if Ran attacked me when I was sailing to Niflheim. Um, there's a lot of pressure and it gets more intense the deeper you get in the ocean, and you need, like, protective gear to keep from exploding or whatever. And if you go up too fast to let the pressure changes happen gradually, you get really sick. It feels like there's no, like, gradation here." He pokes the water again.