Complex sentence: The bulk of the Mainland is west of Kirkwall and is low-lying, with coastal cliffs to the north and west and two sizeable bodies of freshwater, the lochs of Stenness and Harray.
Split into simpler sentences: The bulk of the Mainland is west of Kirkwall. It is low-lying, but with coastal cliffs to the north and west and two sizeable bodies of freshwater, the lochs of Stenness and Harray.