At the Lusaka sewage ponds, two teenage boys plunge their hands into the dark brown sludge, gathering up fistfuls and stuffing it into small plastic bottles. They tap the bottles on the ground, taking care to leave enough room for methane to form at the top. A sour smell rises in the hot sun, but the boys seem oblivious to the stench and the foul nature of their task.

This year, people will get to see the Grand Canyon in a new way. A new horseshoe-shaped glass bridge will extend, or stretch out, over the edge of the canyon. Tourists standing on the bridge will be able to look down and see the Colorado River 4,000 feet below. That's about four times the length of the Empire State Building from top to bottom.