A Great Ridge is a feature any polyhedral planet has. It is equivalent to the edges of the associated polyhedron. Because Dwaia is a cubal planet, it has 12 Great Ridges. You would thinks that the gravity at such places would point to the center of the planet, making these ridges feel like giant mountains, but actually, it just sort of glitches out like some shittily programmed Unity game. It was never said that the gods actually knew what they were doing.