This story appears in the February 2018 issue of National Geographic magazine. Earth’s highest city, its most crowded city, its most polluted city: Geneva-based photographer Steeve Iuncker ...

The Earth's interior is composed of four layers, three solid and one liquid—not magma but molten metal, nearly as hot as the surface of the sun. The deepest layer is a solid iron ball ...

We looked inside some ghost cities with the latest in satellite technology, including time-lapse images, to show what’s making progress and what isn’t. More from Travel China still has a ...