It wasn't for any reason. Just out of no reason. I thought it would be fun if there is a lounge café in the free space between the twin towers, and if the café revolves as it moves vertically like an elevator. While the outside landscape is constantly changing and revolving, we listen to music over a cup of coffee, appreciate the interior decoration and props, and see the exterior scenery as if we were watching a panoramic movie. So how many birds can be caught on a stone? The title was originally called "the Elevator Café." It was abbreviated as "the El Café." Of course, "café" means coffee in French. However, in the meantime, I interchanged Café's C and El's l into "the Eclafé", which may give an exotic feeling, but finally decided to be "El DoraDo". This word implies everything that characterizes our café. The first word "El" means "Elevator", and the second part "Dora" means "turn" in Korean. Do(島), written in Chinese character, naturally means an island. We have to cross a bridge to get to this island. Our El DoraDo is also reminiscent of Spanish El Dorado, meaning "the golden place", and is often used to refer to a utopia. As "El" also means "The" in Spanish, we do not add "The" to our El DoraDo. It is just "El DoraDo." To maximize El DoraDo's panoramic view, it must first be shaped like a flying saucer and have transparent walls all around. Going up as high as possible, we get a much wider panoramic view. Structurally independent El DoraDo, moving vertically and revolving, is decided to be built in the space between the tall twin buildings. Why? Because it's my own imagination. Rather, the space between most of the twin buildings in the world is free, which is advantageous in terms of space utilization, and it is structurally advantageous because the twin buildings can support El DoraDo. It would be less costly to be supported by separated buildings than to support El DoraDo by itself. The key is to find appropriate twin or triple buildings. Existing twin buildings have already completed structures for themselves, so adding El DoraDo between these buildings would be cumbersome because some or more of the existing structures must be modified for El DoraDo. Then, if we collaborate with someone or some company that wants to build twin buildings, we can put it in the original design. This book tells a story of building and running El DoraDo under this circumstance. It is assumed that El DoraDo is supported by twin or triple 50-story buildings. The buildings also supply electric power for El DoraDo to move up and down and for other power consumption. So let's board El DoraDo and have a cup of coffee there for over an hour. When will we ride it? There is no problem if we board before the departure of El DoraDo from the mother ship, from the shopping mall of the buildings. But can we ride El DoraDo while rising and revolving? It is of course possible. Now let's say our El DoraDo is at the level of the 40th floor of the supporting buildings. First, let's go to a nearby elevator in the shopping mall. There are many elevators belonging to the shopping mall and to the supporting buildings to carry us to El DoraDo. They are just ordinary elevators. However, the sides of the elevator facing toward El DoraDo are made of glass, so we can see if El DoraDo is nearby. The elevator ascends as fast as it hits, then stops on the nearest floor to the present level of El DoraDo. There we can get a transit lift that will guide us to the entrance to the bridge connecting to El DoraDo. Soon, the transit lift is separated from the high-speed elevator and docks with the gate to the bridge to El DoraDo. After crossing the connecting bridge, we enter El DoraDo. If the entire El DoraDo body is revolving, it may not easy for us to board. To safely board in a revolving state, El DoraDo has dual ring-shaped decks, inner revolving one and outer non-revolving one, as shown in the cover figure.