Complex sentence: The Île de la Cité, one of two islands in the Seine within the city of Paris (the other being Île Saint-Louis), is the centre of Paris and the location where the medieval city was refounded.
Split into simpler sentences: The Île de la Cité is one of two islands in the Seine within the city of Paris (the other being Île Saint-Louis). It is the centre of Paris and the location where the medieval city was refounded.