Answer: Peru

Typically, when you find a settlement that is inaccessible save for approach by boat or plane, the settlement is a small affair sprung up at some point in the past to cater to, say, fur trappers or loggers. It’s rare to find a place unconnected to the outside world by rail or road that is also a large and bustling city.

In that way, Iquitos, Peru is a curiosity nestled in the Amazon jungle. The area has long been inhabited by native peoples, but the city itself was established by Jesuits in the mid-18th century. In the late 19th century, the rubber boom attracted thousands of people to manage and work the rubber factories as well as supply all those workers with goods and services. Later, in the 20th century, diversification of its economy and tourism further expanded the size of the city and today the population is approximately 472,000 strong.

Not a bad growth curve for a location that is only accessible by the Amazon river or plane, discounting a road that connects the city to the small town of Nauta further inland which, in turn, has no road-based connection to the outside world either.