kilometre

And from six kilometres up, the landscape looks bizarre: there are very few large-scale circular features like that in the world.

The top speed of those boxes is about 14 kilometres an hour and they pass within five millimetres of each other when they move.

What this means is that everything in an area of 500 square kilometres that is able to burn, starts burning.

For the best view, you need to go a few kilometres that way.

Remarkably, Dragon's Breath is part of a vast cave system that extends beneath the Kalahari for thousands of kilometres.

If humans had a base on Mars, we couldn't keep popping back 225 million kilometres - a journey likely to take around seven months - to have children on Earth.