indescribable

Impossible (or very difficult) to describe.

He proved it with indescribable mathematics.

Presently the men set up the melancholy little chant that I had heard on the first night when we were captured in the whaleboat, and the effect produced by their voices was very curious, and quite indescribable.

Exceeding all description.

Our hotel had an indescribable view of the Bay of Naples.

The time was when, had such an idea entered her mind, it would have been torture indescribable and agony the most intense; but then, subdued as was the usual warmth of her temperament, an awful suspension seemed to hold her feelings in control.