Complex sentence: Cornwall forms the westernmost part of the South West Peninsula of the island of Great Britain, the very tip of which is Land's End, the furthermost western point of the island of Great Britain; the southernmost point is also in Cornwall at Lizard Point.
Split into simpler sentences: Cornwall forms the westernmost part of the South West Peninsula of the island of Great Britain. The furthest south-western point of the island is Land's End; the southernmost point is Lizard Point.