The secret base

Once upon a time there were two kids. They liked acting out games in real life. Their interest started when they built a tree house with their farther. They modified it a lot and it became the most treasured tree house in the neighborhood. They built a bunch of tree houses and connected each house with tension bridges secured by sets of ropes. This allowed a system of leaving a house easily. As the kids became better engineers the tree house system connected cities. Many people thought of these bridges as a pedestrian walkway similar to a subway but provided a view. Some families would try to walk across countries sleeping and eating at the tree house "stations." Certain people even created restaurants that spanned across a couple of bridges with the main kitchen in a building and waiters delivering food. The bridge network often went over major hotels and were connected with them. Later, more and more big cities adopted the bridge network. However none had trees tall enough to match the height of skyscrapers. The children of this city thought that they could place the bridge out at a lower level to connect with the skyscrapers. As technology grew the bridges were as cheap as possible but also as strong as possible.  The bridge was so good that people began to set tolls if people wanted to enter at a certain entrance. Now, buildings were not only priced for their quality but also the number of bridges that intersected at the station. Generally, the bridges followed the routes of freeways or highways. Sometimes, smaller bridges were funded by building owners to increase the number of bridges intersecting. It later had great organization so that only certain routes would be tolled. Certain cities also developed around bridge stations they were often named after the children originally with this idea.