unpierceable

And is he then unpierceable," quoth she,   "That neither force nor foe he needs regard?

From Jerusalem Delivered by Edward Fairfax

"Estelle is a courageous woman and discreet with the unpierceable reticence of spontaneity."

From Balloons by Elizabeth Bibesco

Here the unpierceable walls were washed every morning by an automatic sluice.

From The Ball and the Cross by G. K. (Gilbert Keith) Chesterton

Sorrow, sin, pride, shame, ambition, failure, obstinacy, ignorance, selfishness, forgetfulness—enough to make ye veil your radiant faces in unpierceable clouds to hide forever the sight of so much crime and misery.

From A Romance of Two Worlds by Marie Corelli

It was a very trying experience, as the river was absolutely unknown to me; the darkness was "unpierceable by power of any star," and the river was treacherous in itself for small boats.

From My Life in Many States and in Foreign Lands Dictated in My Seventy-Fourth Year by George Francis Train