Complex sentence: Even when the mills were still operating, there were remote stretches of wild bluffs and overarching trees; now the old mills had become romantic and picturesque, with mossy stone walls suggesting medieval ruins.
Split into simpler sentences: Even when the mills were still operating, there were remote stretches of wild bluffs and overarching trees. Now the old mills had become romantic and picturesque, with mossy stone walls suggesting medieval ruins.