One of the most popular works of the word, especially in the Argentine Republic, allows to designate the railway system that operates in large cities and that is built underground, in simpler words, underground, and that exclusively transports passengers in mass transit from one side to the other of the city in question and also to its closest surroundings.
It should be noted that this type of transport system offers a service of different lines that form a network, in which each line is concerned with connecting two distant points of the city and doing so by stopping at different stations, not very far from each other, and that they are arranged at normally regular distances. Similarly, it is common for one or more of the stations on each line to connect directly to a bus or train terminal with the mission of accelerating the transfer of passengers from the city where they normally work to the suburban areas in which they live.
The word underground, originated from the Latin term “subterranĕus”, is composed of the prefix “sub” in the sense of “below” and by “ earth ” = “earth”, its meaning being that which is below the earth's surface. Designates anything or activity that is found or performed underground, such as underground excavations, underground treasures, or underground mines.
Now we must bear in mind that there are underground cities that; They are a network of tunnels that connect buildings, generally in the central area of a city, such as office buildings, shopping centers, train and subway stations, theaters and other facilities. Normally, an underground city is accessed through the public space of any of the buildings that connect it, and sometimes it also has separate entrances.
Underground cities are especially important in places with a cold climate, as they allow their citizens to enjoy the services of the center without taking into account climate problems.
Underground cities are similar in nature to the ceiling systems, and may also include interconnected buildings through elevated walkways or footbridges to the level of the ground, rather than subways.
