Where is the city with a population of more than 500 thousand people that tourists cannot reach by road?

The population of the city of Iquitos in the Peruvian Amazon, together with its suburbs, exceeds 500 thousand people. This is the largest city on the planet, which can not be reached by road – only by river or air transport – except for the highway to the city of Nauta 100 km long. The heyday of Iquitos came during the rubber rush of the late 19th century, but now its economy is quite diversified, besides the city attracts a large number of tourists. There are plans to build a road to Sarameriza, which would connect Iquitos with the Peruvian transport network, but so far only on paper.