It doesn't take too much for a city to be considered a tourist hotspot – a few interesting landmarks and perhaps some attractions to keep little ones busy. But for a city to become a hub for Ultra High Net Worth Individuals (UHNWIs) – people who are worth more than $30 million (£23m) – there needs to be a perfect storm of business opportunities, thriving culture, and a certain je ne sais quoi. Each of these cities have all of those things in spades. So, read on to find out where the richest people in the world call home...