It is one of the most baffling questions that scientists can ask: how big is the Universe that we live in?

Horizon follows the cosmologists who are creating the most ambitious map in history – a map of everything in existence. And it is stranger than anyone had imagined – a Universe without end that stretches far beyond what the eye can ever see. And, if the latest research proves true, our Universe may just be the start of something even bigger. Much bigger.