A few years ago, a NASA scientist named Geoffrey Landis, who also writes science fiction, suggested an interesting way to colonize Venus, the second planet from the sun and actually closer to the Earth than Mars.
At first glance this seems to be an eccentric idea, politely speaking. While Venus was once thought to have an Earth-like environment beneath its world girdling clouds, its surface is in fact a real life analog to Hell. The surface of Venus has an atmospheric pressure of 90 times that of Earth and a temperature that is often enough to melt lead. Even robotic landers have not lasted on Venus for very long.
But the territory that Landis is looking at actually exists about 50 kilometers above the surface of Venus. Both the atmospheric pressure and temperature is roughly that of Earth in the skies over Venus.
Of course there are drawbacks, such as the fact that the atmosphere of Venus is comprised on CO2 laced with sulfuric acid. But this also means that a bubble filled with a nitrogen/oxygen atmosphere would actually float in the skies over Venus since it would be lighter than the air surrounding that planet.
There are certain problems involved in creating floating cities over Venus. They would have to be built of substances that are resistant to the corrosive effects of the sulfuric acid. Also, the prevailing winds over Venus tend to be powerful, running about 350 kilometers an hour.
If these and no doubt other problems could be solved, what would colonists in the skies over Venus actually do? One idea would be to figure out ways to terraform the planet, so that the surface would once again become habitable. Because of the thickness of the atmosphere of Venus, the task would be formidable, consisting in part of the largest carbon capture operation ever conceived. However people, perhaps a century or two hence, who have the wherewithal to live in the skies over a planet could also accomplish its transformation into a new Earth.