planet Venus

At 50-58 Km above the 'ground' the temperature ranges from boiling water to freezing water - and air-pressure ranges from a factor of three times Earth-normal to a third ... clouds form high in this strata, and rain continually into the reboiling depths ... ordinary nuclear-powered air-craft may ply this region, but the nuclear fission fuel must first have come from other planets and moons more accessible - a necessary accessioning and transportment of Earth-stores of plutonium ²³⁹Pu by the GNSC.

Just below this habitable level, the atmosphere of Venus is a special nuclear environment pliable by small-winged heat-pump-cooled 'sub' planes capable of leaping up to the tenuous 'living' heights, and diving to thicker-pressured scorching depths.

At mid-level, where the air is Earth-balmy, we might build clear-bubble-encased floating cities on foamed wood base ... the wood resource is continually growable topside in the CO₂ and water vapor atmosphere, and the foam needs only be sealed against the larger gas molecules - it may float permanently charred below. Placed poleward, beyond 60 deg North and South of the equator, the gravity-level sunlight intensity is Earth-tropical, the atmospheric trade-winds still warm and velocity slow enough to require minor adjustment to stay in sun-relative place, if any: Catching a convection drift may suffice to keep such a city on the sunny-side: And all-day sun allows further poleward situation -- thin-film pole-side mirrors, under domes, may enhance crop growth.

One of the primary reasons for venuforming, but not terraforming Venus, is that Venus may have had sentient inhabitants, likely including dinosaurial long before Earth had dinosaurs. The eonic interval may have been brief: as soon as Venus magmas cooled, and before the sun gained its final brightness estimated by solar astronomers to be now 40% more than during the early billion years ... so while Earth may have had an ice age in the early 1-3 billion years, Venus may have been just very warm but liveable-- outside the 45° latitudes, even to the poles which having no significant tilt had fairly steady year-round temperatures lasting billions of years even till the final conversion of the entire atmosphere....

Because Venus is slightly smaller, 0.82 Earth-mass, it cooled slightly faster than Earth ... if the sun did not become visible too soon in the solar nebula, then Venus may have cooled to dinosaurial-supportive temperatures, just before Earth did about 300 million years ago. [If dinoaurs came to Earth from somewhere, Venus is choice] More likely though the early ocean bio-life flourishing on Venus once the surface cooled below boiling hot, about 4 billion years ago [3.5 billion for Earth], thrived until the breaking-through sun-warmth reheated the surface, and re-boiled-away the oceans - then atmospheric heat-containment by ocean-worths of water, 'hot-housed' the surface, converting all carbon-based bio-forms by the water-gas reaction to carbon-dioxide and hydrogen ... the hydrogen H₂ quickly escaped the lower atmosphere, and was driven-away by sun-light and solar-winds into space, leaving Venus with its present burden of CO₂ air, and its 'run-away-hot-house' temperatures, melting lead [metal] at the equator.

Civilizations would have been literally bi-polar, crossing the equator only during the 'weeklong' evening and morning (time not days) between the 'twomonthlong' winter-night and summer-day, somewhat like Earth's polar winters and summers but much warmer in the summer for a total melt, And probably transient for that reason-- to stay on the pleasant dayside: Farming would have consisted of planting after melt in the spring-morning, tending the 'twomonthlong' day, and harvesting in the fall-evening ... very similar to Earth farming.... Toward the end of the Venutian clemency era civilizations could have removed to the poles (where its last artifacts might remain) for stability, and farmed the fringes.... Eventually Venutians would have attempted Earth... possibly as early as the dinosaur era 100-million or billions of years ago, but probably also lived around the poles, making forays tropicward only for hunting.... (The Venutians could have studied Earth dayside from permanent winter observatories as Venus rotates synchronous to Earth's position.)

However, it may be possible to fairly quickly terraform Venus: one theory for its anomalously high surface temperature is the formation of bond-energetic molecules high in the atmosphere, either presently above the clouds or recently below the clouds, which [molecules] then drift down to the surface where by catalysis on the surface, or by extreme temperatures near the bottom, decompose, releasing the bond energy content, and maintaining the temperature: a catalyst applied at the same height in the atmosphere might prevent such or early release the energy, allowing the clouds and surface to cool and reform to terraform capability by teams entering at the then-cooler poles.