From (where else?) the latest Rocketpunk Manifesto blog entry, discussing the colonization of Venus:
To my surprise there has even been some credible discussion of colonization - not of the hellish surface but the upper atmosphere, with aerostats AKA balloons. At 50 km above the surface the atmospheric pressure is equal to Earth's, and temperatures are near the human comfort zone, 0-50 C. Human breathing mix is a lifting gas on Venus (with roughly half the lifting power per cubic meter of helium on Earth), so the entire gas envelope can contain breathing air.
I love this image: a magnificent floating city inside a gigantic bubble of air, drifting on poisonous winds, 50 kilometers over hell. Humanity collectively lifts a technological middle finger to the hostile universe, signaling our intention to thrive everywhere....