Complex sentence: There has been human activity on the site since the Upper Palaeolithic; during the Victorian era, it was heavily quarried, and in recent years tourism has become significant--it receives more than one million visitors annually.
Split into simpler sentences: There has been human activity on the site since the Upper Palaeolithic. During the Victorian era, it was heavily quarried, and in recent years tourism has become significant--it receives more than one million visitors annually.