Robin, Martin and Alex discuss The Line - Saudi Arabia's $1 trillion (or more!) megacity of the future in the desert. Intended to be home to 9 million people, this continuous skyscraper will stretch for 170km (105 miles) and supposedly be self-sustaining on renewable energy, with no cars and all the amenities you need. But will this dream project actually become reality? And if it does, will it be worth the controversial costs? Plus we reveal what we learned this week and respond to your comments!