Thickening the edges of the tetrahedron yields a Riemann surface of genus 3 with a holomorphic action of the tetrahedral group. M. Oka asked what is the defining equation of this Riemann surface as an algebraic curve. In this talk, I will describe the solution of M. Oka¡Çs question. Unexpectedly the solution forms a 1-parameter family with a sporadic hyperelliptic curve. The image under the moduli map into the moduli space of genus 3 curves is determined. It is a curve passing through the Fermat point and self-intersecting at the Klein point. The universal family around the Fermat point is also described.