Hong Kong may be best known as an urban jungle, but it's also home to dozens of hiking paths that offer breath-taking views of the city's natural surroundings. In 2012, Andre Blumberg created the Hong Kong Four Trails Ultra Challenge (HK4TUC), a marathon of four Hong Kong ultra-distance trails totalling 298 km over three non-stop days. Chronicling the 2021 edition of what is now one of the hardest ultramarathons on the planet, Robin Lee's riveting feature-length sequel to his award winning sports documentary shows runners facing a gruelling endurance test.—HKAFF