A while back, after some thinking about where in our solar system humanity could colonize, I had a realization. The most Earth-like place in our solar system (other than Earth, of course) is Venus. Brutally hot, super-pressurized, highly-acidic Venus. How could that be? Well, the atmosphere of Venus has a lot of pressure. In fact, to get the same pressure on Earth, you have to go underwater... deep underwater.
All of that got me thinking... we build stuff all the time that floats on the oceans. We even have balloons whose low density and pressure allow them to float through our atmosphere here on Earth. Could we build something that would "float" above Venus in the same way? And how high would it have to float in order to have Earth-like air pressure?
Fortunately, I don't have to do that math on that myself. Nancy Atkinson over at Universe Today reports that Geoffrey Landis of NASA Glenn agrees with me about colonizing Venus, and he's already done some of the calculations. Apparently, about 50km above Venus the air pressure is roughly the same as the surface pressure here on Earth. Even better, at that height, the temperature is also in a much friendlier range between 0°C and 50°C.
That doesn't mean that Venus is without it's problems. The atmosphere is still highly acidic, for one thing, and any floating structures we try to place there would need to be highly resistant to sulfuric acid. Not only that, but with still one atmosphere of pressure, the floating structures we could place there would likely be thoroughly battered by turbulence, constantly bobbing up and down as air pressures and currents bobble the bubble (so to speak).
For those reasons, it seems more likely that the first structures we would emplace at Venus would be more likely to be observatory facilities, unmanned scientific facilities to study the atmosphere in preparation for more advanced structures later.
In any event, and floating structures on Venus are decades (at best) or centuries (more likely) away.