Colonize Venus - Our closest planetary neighbor is the perfect place to build cities floating in the sky. According to Geoffrey Landis, we’ve been looking at planet Venus all wrong regarding its potential to become a human settlement. It’s rocky surface, which features enormous pressures and temperatures too extreme for human comfort, should be looked at like the floor of a vast ocean; and unlike Mars (0.38g), Venus’ gravity is very close to that of Earth (0.9g).
[…] at the rock surface the venusian atmosphere is no longer gaseous, but is rather a supercritical fluid (neither liquid nor gas), it is actually technically correct to think of Venus as enveloped in a global carbon dioxide ocean.
Since the atmosphere of Venus is predominantly carbon dioxide, breathable Earth air, which is lighter, becomes a lifting gas. An inhabitable air-filled base or indeed an entire city can thus float effortlessly.