World's Busiest

Discover Hong Kong, where space is at a premium and real estate is the most expensive in the world. Ade heads into the high rises to find people living in tiny spaces no larger than a cupboard. This former British colony, handed back to the Chinese in 1997, is a city driven by trade and commerce and Dan discovers how it's adapting to life in China's embrace while Anita learns about the city's traditions - from bamboo scaffolding to banishing bad spirits on the daily commute. How does this city of contrasts manage the delicate daily balancing act that keeps it on track?

The hidden systems that run Mexico City, a sprawling megalopolis of over 22 million people.

Uncovering the hidden systems running Moscow - a city forged by power and politics.

Uncovering the hidden systems running Delhi - hot, hectic and home to 26 million people.