concavity

The valley looks utterly serene now – a spacious concavity lying between pine-clad peaks.

峡谷是一大片洼地，坐落在松林覆盖的山峦之间，此时显得寂静无声。

There is the slightest hint of concavity that allows the bottle to fit snugly in my grip.

瓶子几无凹处，不容易握住。