The Drownyard is a reef in the sea of near Nephalia on Innistrad where many ships were lost. Here, the crazed lithomancer Nahiri constructed a ring of cryptoliths around a stirring in the water. She made use of Gisa's ghouls to build this so-called Drownyard temple. All the other cryptoliths scattered over the plane point towards this location.
The findings of Tamiyo support a connection between the temple and an invisible object of significant mass in the sky. This is most likely a new astral body, an eldritch moon of sufficient size as to provide a gravitational pull able to disrupt the normal patterns of both the tides and magical energy.