After 15 years of developing 'Killzone', Guerrilla Games made the bold decision to move in a new direction and focus on a brand new genre and IP, 'Horizon Zero Dawn'. To Guerrilla's character team, the massive open world of 'Horizon Zero Dawn' was a giant blank slate with unlimited potential, but from another perspective it provided a host of new challenges. How could they rise to the creative challenge of filling a world full of new and distinct peoples without second guessing themselves and succumbing to uncertainty? How could they build enough content to fill the massive open world without losing the small-team culture they spent years developing? How could they do useful work in an environment where everything, story, mechanics, world building, is constantly evolving? This lecture discusses how Guerrilla Games tackled these challenges, with honest reflection on their successes and mistakes.