Zac and Darin get an up-close look at Iceland's renewable energy efforts; they also soak in a spa, sample reindeer meat and view natural wonders.

Before heading to Paris to learn about its tap water system, Zac joins friend Anna Kendrick for a lesson in H2O from a water sommelier in Los Angeles.

In Costa Rica, Zac and Darin try out life in a swanky eco-village committed to a small environmental footprint; they visit a wildlife refuge and enjoy a zip-lining trip.

Sardinia boasts a notable number of centenarians, causing Zac to rethink his views on nutrition as he ponders how the locals live such long healthy lives.

Zac and Darin head to Peru to delve into potato cryopreservation, biopiracy and the sport of sandboarding.

In the wake of Hurricane Maria, Zac explores sustainability in Puerto Rico where he meets chef José Andrés, milks a goat and eats ceviche.