Complex sentence: The cliff above the beach, Boncan Dinas, has an Iron Age hill fort, Dinas Dinlle, that has been eroded by the sea, such that only a double semi-circular rampart remains.
Split into simpler sentences: The cliff above the beach is known as Boncan Dinas and is occupied by an Iron Age hill fort, Dinas Dinlle. This fort has been eroded by the sea, such that only a double semi-circular rampart remains.