- Curving Inwards - Dented inwards - Hollow - Opposite to convex - Prisoner in front of underground chamber looks depressed - Trick cavern that’s curved inwards - Hollow and curved or rounded; vaulted; -- said of the
interior of a curved surface or line, as of the curve of the of the
inner surface of an eggshell, in opposition to convex; as, a concave
mirror; the concave arch of the sky.