hypogeum
An underground room or cavern (also used figuratively).
Contour: the unique parameters of Karen’s body – beckoning vents of mouth and vulva, the soft hypogeum of the anus.
Where it comes from
From Latin hypogaeum, from Ancient Greek ὑπόγειον (hupógeion), a noun use of the neuter singular of ὑπόγειος (hupógeios, “underground”).
Adapted from the Wiktionary entry hypogeum (CC BY-SA 4.0).