In this final episode we complete our journey, travelling back from the March equinox to the end of June. Kate Humble is in the Arctic at a place where spring arrives with a bang, whilst Helen Czerski chases a tornado to show how the earth's angle of tilt creates the most extreme weather on earth.

For the last 40 years, the photographer Sebastião Salgado has been travelling through the continents, in the footsteps of an ever-changing humanity. He has witnessed some of the major events of our recent history; international conflicts, starvation and exodus. He is now embarking on the discovery of pristine territories, of wild fauna and flora, and of grandiose landscapes as part of a huge photographic project, which is a tribute to the planet's beauty". Sebastião Salgado's life and work are revealed to us by his son, Juliano, who went with him during his last travels, and by Wim Wenders, himself a photographer.

Professor Richard Fortey delves into the fascinating and normally-hidden kingdom of fungi. From their spectacular birth, through their secretive underground life to their final explosive death, Richard reveals a remarkable world that few of us understand or even realise exists - yet all life on Earth depends on it. In a specially-built mushroom lab, with the help of mycologist Dr Patrick Hickey and some state-of-the-art technology, Richard brings to life the secret world of mushrooms as never seen before and reveals the spectacular abilities of fungi to break down waste and sustain new plant life, keeping our planet alive. Beyond the lab, Richard travels across Britain and beyond to show us the biggest, fastest and most deadly organisms on the planet - all of them fungi. He reveals their almost magical powers that have world-changing potential - opening up new frontiers in science, medicine and technology.

The film is the inside track on the World's most influential weapon. For over a thousand years this weapon dominated the battlefields of Japan, instilled fear and terror into every enemy it faced, and created a new spiritual way of life that lasts through to the present day. The Samurai sword – a weapon so technologically perfect in structure, so formidable in strength and so beautiful in creation. For the first time unique access has been granted and we travel into the core of the ancient foundries, sword-smiths and fighting schools to reveal what makes the so-called perfect sword. This is a no holds barred look at one of the most iconic man-made objects ever forged.

What if we could travel not just through space, but through time itself? If you could travel through time, would you change the past or the future? What if you found it couldn’t be changed? What price does the time traveller -- and the people they are closest to -- pay? This is a journey from H. G. Wells' The Time Machine through ideas like The Grandfather Paradox and The Butterfly Effect to the professional time traveller that is the ever popular Doctor Who. Steven Moffat, David Tennant, Karen Gillan, and Neil Gaiman offer a unique perspective on the Doctor. Edward James Olmos reveals the hidden meaning of the language he created for the vision of the future that is Blade Runner. Bob Gale and Christopher Lloyd take us behind the scenes of Back to the Future, while Ed Solomon describes the joy of solving a time travel conundrum for Bill & Ted’s Excellent Adventure. But what would be the physical and emotional cost to the time traveller? Audrey Niffenegger explains what inspired her novel The Time Traveller’s Wife. And what if someone from the future tried to travel back in time to warn us? Would we believe them? From the apocalyptic tones of 12 Monkeys to the drama of Quantum Leap and the comedy of Groundhog Day, time travel is a subject that has been irresistible to the creators of every type of science fiction.

Of the Seven Wonders of the Ancient World, the Hanging Garden of Babylon is the most elusive of these constructions of classical antiquity. While traces have been found of the Great Pyramid of Gaza, the Temple of Artemis at Ephesus, the Statue of Zeus at Olympia, the Mausoleum of Halicarnassus, the Colossus of Rhodes and the Lighthouse of Alexandria, centuries of digging have turned up nothing about the lost gardens of Babylon – until now.
Why, in the nearly 3,000 years since the gardens were presumably built, has no archeological evidence ever been found to support their existence? Is the Hanging Garden of Babylon a myth or a mystery to be solved?
Travel with Dr. Stephanie Dalley of Oxford University’s Oriental Institute and author of The Mystery of the Hanging Garden of Babylon, to one of the most dangerous places on earth, as she sets out to answer these questions and prove not only that the gardens did exist, but also identify where they most likely were located, describe what they looked like and explain how they were constructed.