Complex sentence: Before the extension was built, the Jubilee line terminated at: the section between Charing Cross and is now unused for passenger services but is maintained for emergency use (and at least one misdirected passenger train has ended up there).
Split into simpler sentences: Before the extension was built, the Jubilee line terminated at. The section of Jubilee line between Charing Cross and is now unused for passenger services but is still maintained for emergency use (and at least one misdirected passenger train has ended up there).