A person or thing that cannot be known or understood; something unfathomable or puzzling.

完全不懂的人，不了解的事：无法认识或了解的人或物；深不可测或迷惑不解的东西。

youdao

Amidst many equally or even more ferocious African conflicts, what made Darfur enthralling to many Westerns was neither its horrific intensity nor was its unfathomable brutality.

在许多同样的甚至更凶猛的非洲冲突中，对于许多西方人来说达尔富尔迷人的既不是什么可怕的强度也不是深不可测的暴行。

youdao

Somehow, contrary to what every consumer with an Android phone, iPad or unfathomable access to diverse programming content experiences every day, they find nothing but misery and despair.

FORBES: Creating a "Politics of Abundance" to Match Technology Innovation