Complex sentence: Monreale forms its own archdiocese and is renowned for its Norman-Byzantine cathedral which is a UNESCO World Heritage Site as part of a group of nine inscribed as Arab-Norman Palermo and the Cathedral Churches of Cefalù and Monreale.
Split into simpler sentences: Monreale forms its own archdiocese and is renowned for its Norman-Byzantine cathedral. This has been designated as a UNESCO World Heritage Site, part of a group of nine inscribed as Arab-Norman Palermo and the Cathedral Churches of Cefalù and Monreale.