Man's Future Beneath the Sea (1968)

This image from the 1968 book Explorers of the Deep: Man's Future Beneath the Sea depicts the inevitable colonization of the ocean floor.

Man has only two vast, natural frontiers left to him: outer space and the oceans, both of which are still virtually unexplored and unexpoited. In the years to come, technological breakthroughs will make possible a major escalation on the part of the world's oceanographers to develop the resources of the oceans for the benefit of mankind. The new realm of hydrospace will provide thousands of new job opportunities and bring about the birth of dozens of new industries as our oceanic engineers perfect the techniques to dive deeper and stay longer under the surface of the seas.

See also:
Sea City 2000 (1979)
Undersea Cities (1954)
The Future World of Transportation

Undersea Cities (1954)

Rather than a floating city, today we have an image of undersea cities from the book Out of Time: Designs for the Twentieth-Century Future.

The book says that the image was published on the cover of if magazine in January of 1954. The most perplexing choice of the artist is why some of the "undersea cars" are driving on the ocean floor. It doesn't seem very practical but I'm sure that it helped 1950s audiences picture such an environment as familiar or more desirable.

See also:
Sea City 2000 (1979)