Four billion years ago, Venus, Earth and Mars each held the promise of supporting life, with oceans, supportive climates, and the chemical ingredients of biology. Over the eons since, Mars lost its atmosphere, turning ever colder, while Venus entered a death-spiral of ever-increasing heat. But, 50 km above its desolate surface, the cool cloud tops of Venus offer a potential refuge. This zone is protected from cosmic and solar radiation overhead and the blistering surface temperatures below. Solar powered ships and habitats could effortlessly float there, sailing the brisk winds that circle the globe. That has inspired visionary engineers and scientists to take the first steps toward settling the 2nd planet from the Sun.