Zenpōkōenfun
Zenpokoenfun is an architectural model of Japanese ancient tombs (Kofun), which consists of a square front part (前方部, Zenpō-bu) and a circular back part (後円部, Kōen-bu). The part connecting the two is called the middle part (くびれ部, Kubire-bu), which looks like a keyhole when viewed from above.