A steady stream of tourists come to Yakushima Island each year to gaze up in awe at Japan's most famous tree. The Jomonsugi cedar exceeds 16 meters in circumference and is thought to be more than 2,000 years old. Is it the country's largest? And what lies up in the treetops hidden from view? The Darwin crew joined a special research team traversing the dense undergrowth in their four-year quest to locate other massive cedars and document the incredible ecosystem thriving in the tallest branches.