Unfathomable (adjective)

Incapable of being understood, grasped, or explained; mysterious; deep.

Origin:

From un- (not) + fathomable (able to be fathomed, able to be understood or grasped).

Examples:

1. The mysteries of the universe are unfathomable.
2. The unfathomable depths of the ocean have yet to be explored.
3. The pain and suffering of the victims is unfathomable.
4. The genius of the artist's work is unfathomable.
5. The complexity of the human mind is unfathomable.