The city of Mumbai, India, is home to nearly 14 million people.
To put that number in perspective, it's like more than the total population of Illinois all packed into an area smaller thanChicago.
And that's not counting the estimated 10 million more people that live in Mumbai's sprawling suburbs. In parts of the city there are more than 1 million people per square mile -- more than any other spot in the world.
"It's just like the whole city is like alive and kickin'," Pooja Batra, former Miss India, told "Good Morning America." "It has an essence. It has a heart. It has a character."
To keep the heart of the city beating, Mumbai sports an impressive infrastructure, including one of the world's largest network of trains and shuttles that carries more than 6 million people daily.
The seaside city is also the nerve center of India's economy and workplace to thousands of business people.
Lunchtime is a spectacle of human logistics.
Then, 5,000 men who call themselves "tiffinwallas" deliver 175,000 lunches to working people in Mumbai each day using a unique and complicated conveyor-beltlike system. The tiffinwallas also use bikes, buses and trains to get home-cooked meals perfectly sorted and shuttled through Mumbai traffic to their customers.
Even though the effort is massive, the tiffinwallas purportedly make mistakes only once every couple of months.
Such attention to accuracy earned the tiffinwallas a Sigma Six rating from Forbes, the biggest worldwide prize in efficiency.
Efficiency is not the only reason Forbes has taken notice of Mumbai -- the city is also home to 20 of the world's billionaires.
But alongside the vast richness and luxurious lives of India's elite is the extreme opposite -- utter squalor in the city's crumbling slums where more than half the city's population lives.
There, the rich literally live on top of the poor. Million-dollar condominiums are stacked on top of shantytowns.
It is a symbolic image for the many who live below who dream of being one of the few who live above.
In a country where so many are lacking, novelist and actress Shobhaa De has led something of a charmed life.
"My world, unapologetically I suppose, is the world of the elite in India. It is a privileged world," De said. "But that does not mean that one doesn't have a conscience and one cannot do something with that privilege. And I try my best."
De referred to Mumbai's massive poor population housed in the cities sprawling slums.
"That's what makes the city so challenging because you have to live beyond that all of that. Here we deal with it. We have our poverty. I'm not saying we deal with it very competently, but we are not in denial about it."
Dev Tank, 22, is not in denial about it at all. He lives in Dharavi, Asia's biggest slum, with more than 1 million people. There, where his family has lived for three generations, most people do not have clean water.
But Tank does not call his home a slum.
"It's more like a community living together, helping each other," he said.
Of course, Tank does not seem like someone who would generally live in a place like Dharavi. He is a college graduate and has a good-paying job at a multinational financial firm.
"If you're not educated, you cannot do anything," Tank said simply.