Complex sentence: To the west lies the Tasman Sea and to the east the Pacific Ocean, joined by narrow and turbulent Cook Strait, which is only wide at its narrowest point, between Cape Terawhiti and Perano Head in the Marlborough Sounds.
Split into simpler sentences: To the west lies the Tasman Sea and to the east the Pacific Ocean. At the southern end of the island these are joined by the narrow and turbulent Cook Strait, which is only wide at its narrowest point, between Cape Terawhiti and Perano Head in the Marlborough Sounds.