I have a vision. Sometime in the future, a peasant in a poor country hears from a friend about a new government project. He gathers together his family, a few bags of seeds, and some farm tools, and loads them into a truck that his brother managed to buy before a random militia killed him. They drive to the site.
The site is a building that covers hundreds of acres. A worker there explains that the building contains farms enough for everyone, and that this worker may have one for 5% of his yield. This is agreeable to our farming family. They are given a card-key (the kind that some fancy hotels give out to allow access to exactly one room), and a pair of sunglasses each, and told to drive the truck into the far part of the building. They are told to bring everything into the room, then put the card into the slot in the wall.
After loading the room up, our intrepid farming leader puts the card into the small slot in the wall, which accepts it. Suddenly, there is a feeling of movement. This entire room is an enormous elevator. It moves for a long time, then stops. With a ding, the doors open to a non-descript room. The card is returned from the slot, and our farming family walks in. The doors close behind them. The elevator leaves with a wirr, presumably back to the surface.
An electronic sign on the wall notes that this is the entrance to this family's farm in the local language. Another sign, this one hand made, informs visitors that they should wear their sunglasses while in the farm. The enormous door, large enough to drive a truck through, has a slot next to it, the same as the
elevator room. Our family puts on their sunglasses and inserts their card. The large doors swing open revealing a light brighter than the sun.
After everyone's eyes adjust, it becomes apparent that this light is coming from the ceiling, which is covered in LEDs. The room is a farm, hundreds of acres in size. In fact, it is the same size as the building, but 20 feet tall. The soil is warm, moist, and composty, but nothing has been planted yet.
With the feeling that their new farm was good indeed, our family gets right to work planting. Clearly this will be a good year, barring no disasters and little government corruption. Gentle music combined with quiet nature sounds fills the air, apparently coming from the walls. The seeds are quickly all planted.
Our family then wishes to return to their dwelling. They close the enormous doors and remove the keycard. They then use the keycard on the wall with the elevator, which returns within ten minutes. They drive the truck into it and insert the keycard into the elevator's slot to indicate that they are ready. The elevator wirrs as it pulls them back to the surface.
Meanwhile at the farm, the pleasant music has been replaced with loud cacophanous sounds that would be quite objectionable to any people present, if there were any. These loud sounds benefit the plants by causing vibrations in the air. (An experiment showed that plants grow best in the presence of loud heavy metal and worst in complete silence.) The light remains on until 6pm local time, at which time it is extinguished. The plants grow in the darkness until 3am, when sprinklers in the ceiling spray them with water for two hours. At 6am, the bright lights are once again lit. All of this happens by automated computer control, without any human intervention.
Some time in the next morning, our farming family returns. Before they open the door, the cacophanous noise is replaced by gentle music and nature sounds. The plants are growing well, our family observes. There are no pests here, no vandalism, and disease has not taken hold, and with care it never will.
Our family doesn't necessarily know this, but there are hundreds, possibly even thousands, of these layers, each one only accessable with the right keycard. Some layers have mechanical equipment, or tanks of water, but most are farms, just like our family's. This building roots deep into the earth, so deep that it can supply the immense energy needs party by purely geothermal sources. Though utlimately, more exotic technologies must supply most of the immense needs, probably around 2-5 megawatts per layer.
Will it happen? Probably not. It's too expensive.