Mars

The very first terraformed world in Sol, which had been undergoing terraformation efforts even prior to humanity's mass expansion across the solar system. Mars was colonized by and for the ultra wealthy, and has the smallest population of any colonized planet despite being larger than most others by area. Due to its small population, Mars has no orbital elevators and most large space ships that visit Mars must rely on atmospheric transport shuttles going to and fro from docking stations in orbit. Unlike other worlds in Sol, Mars was intentionally left underdeveloped and less industrialized. There are over 100 metropolitan areas on Mars with suburbs sprawling out around them, but they are not contiguous. There are many large rural regions in between them, and while most Martians live in the cities or suburbs, the richest of the rich live in castle-like estates far from civilization. Despite its small population and ludicrously high cost of living, Mars is a very popular vacation destination, and its population fluctuates by hundreds of millions each month as tourists come and go. It is a green paradise, Sol's only Eden.