In this episode, Dallas explores how we have been redesigning the planet as we build ever more astonishing places to live. In Dubai, he climbs to the very top of the world's tallest building - over half a mile above the desert sand - to help clean the highest windows in the world; and he explores how desert wastelands have been transformed into bristling forests of skyscrapers as we've conquered the sky and turned it into a place we can call home. In China, the rate of change is accelerating as millions move into the cities; to keep pace, they have learned to erect 30-storey buildings in under three weeks. The world is changing underneath our feet too; Dallas dives beneath Mexico City with one of the two-man team whose unenviable job it is to keep the city sewers flowing, before examining a very new-world solution to this age-old problem.