In between getting an up-close look at Iceland's renewable energy efforts, Zac soaks in a spa with Darin, samples reindeer and views natural wonders.
Before heading to Paris to learn about its tap water system, Zac joins pal Anna Kendrick for a lesson in H20, courtesy of a water sommelier in LA.
Zac and Darin try out life at a swanky eco-village committed to a small environmental footprint, visit a wildlife refuge and enjoy a zip lining trip.
On an island that boasts a notable number of centenarians, Zac rethinks his view on nutrition as he ponders how the locals live such long, healthy lives.
Following a crash course in apple growing, Zac and Darin head to Peru to delve into potato cryopreservation, biopiracy and the sport of sandboarding.
In the devastating wake of Hurricane Maria, Zac explores sustainability in the region, where he meets chef José Andrés, milks a goat and eats ceviche.
After a beekeeping stop on a New York City rooftop, Zac checks out London's pollution-reduction efforts, from wall gardening to trash collecting.
Zac boosts his immune system in the Amazon rainforest before climbing a tree, exploring ayahuasca tourism and watching his dinner wriggle on a plate.