As you no doubt know, and Oya could certainly tell you, there are no 5-sided Pythagorean solids, the minimal three-dimensional structure being the humble tetrahedron. If you draw a line from the geometrical center of the tetrahedron to each of its vertices, you will have a structure that resembles a caltrops. Rendered in concrete. these can be found littering the shorelines of the world. For some reason, they also litter the pages of this chapter of Joshiraku….