He solved the puzzle unfathomably quickly.

The complexity of the human brain is unfathomable.

The ocean is unfathomed, with its depths still largely unexplored.

The unfathomableness of the ocean depths is both awe-inspiring and terrifying.

The unfathomability of the ocean depths is both awe-inspiring and mysterious.

The complexity of the situation was unfathoming.

She is unfathoming the depths of the ocean.

He unfathoms the mysteries of the universe.

I unfathom the complexity of the universe.