I wonder how much the improvements in the technology of the underground influenced Freud's idea of the unconscious. There had always been short tunnels, and miners had dug deeply straight down, but the expansion of mining into whole networks of tunnels was relatively new. In the cities, pipes for both water and sewage were both out of sight, and perhaps correspond to Freud's images of both good and evil coursing around in the depths of the person. Finally, the urban underground transport systems were coming into being popping people up in new locations not visible from the surface.
The circulatory systems of the body had been known about for a few centuries (and the idea that there were important things going on below the skin was far older than that), but the knowledge of them had sharply increased in the 19th C.
The idea "there's a lot going on beneath the surface" had become common, where it had not been before. In the current state of our thinking, we no longer look at those hidden physical forces as deep secrets of life. Subterranean rivers turn out to just be rivers like any other. The forces of circulation are identical to pumps, valves, and tubes in machinery. Most recently in psychology, we are coming to believe that the surface is what is really there. There are no subterranean caverns of the mind. There are forces we are not very aware of, but like Gollum, we find that the labyrinth is eventually just a collection of roads.