Way back in the 1970s, NASA began thinking about constructing large-scale space colonies. The colonies would be placed in stable Earth-Sun orbits (the Lagrange points) and would house upwards of 10,000 people. There were even visions of using the colonies as a service base for orbiting power stations beaming solar power back to Earth via microwaves. Gerald K O'Neill, a Princeton physicist, was a driving force behind many of these ideas.
Artists where commissioned to imagine what these slowly rotating complexes would like (rotation was needed to provide gravity). These visions of "O'Neill cylinders" and our general future in space were gripping and ignited the imagination of more than a few young dreamers. The images are just as beautiful today as there were then.
Here is a link to some of the artwork. They are a reminder of a more optimistic time in our visions for the future.