The deepest hole ever dug by humans is the Kola Superdeep Borehole in Russia, reaching 7.6 miles underground.

Greenland is the world's largest island.

The Nile is generally considered the world's longest river, but some measurements put the Amazon ahead depending on source point.

Ancient civilizations often formed near rivers.

The Millau Viaduct in France is one of the tallest bridges in the world.

The Nile River has supported civilizations for thousands of years.

The Sahara Desert is roughly the same size as the United States.

The Earth's crust is thinner beneath oceans.

Vatican City is the world's smallest country — it covers just 0.44 square kilometers.