Millions of people turned out their lights Saturday night for Earth Hour.
It was created out of concern for the environment.
Lights went out in the Chicago area at 8:30 p.m.
Many city landmarks joined in on the energy-saving initiative, including the Chicago Theater, Navy Pier and the Willis Tower.
Earth Hour started in one city in 2007.
It’s now celebrated in 7,000 cities throughout 152 countries.