Complex sentence: The line included the world's first passenger train tunnel, the 800-yard Tyler Hill Tunnel, and both its portals are still visible, one entrance is behind the University of Kent, and the other in the grounds of the Archbishop's School.
Split into simpler sentences: The line included the world's first passenger train tunnel, the 800-yard Tyler Hill Tunnel, and both its portals are still visible. One entrance is behind the University of Kent, and the other in the grounds of the Archbishop's School.