Night City is a free trade haven in the middle of the Pacific Ocean.
Shiawase Petrochemicals formed the nucleus of Night City in 2031 by creating a set of drilling rigs on a seamount in the Pacific Ocean. Spend time with an atlas and the Internet and pick a good spot. (The great circle route from Japan to Seattle looks like it goes over the Aleutians; the Marshall Islands might also be a good bet.) The initial geological survey suggested there were rich oil fields there, and the management team on the project, desperate for profits, started the process of construction there over the objections of the geology team that a more extensive survey would be required.
Based on the original estimates of the oil there, the value of the petroleum to the plastics and machinery industry would easily pay for the initial set of rigs. (Mere combustion fuel, by then, was usually just created through agricultural processes.) In the environmentally unfriendly era of the megacorps, there was no need to worry about decommissioning such things— abandon-in-place structures would show better profits in the short term, all the way up to times the management team had their early retirements planned.
However, it turned out that the rosy initial assay was not representative of the actual contents of the field, and heads rolled at Shiawase Petrochemicals. The lucky ones arranged quiety extractions while the infighting started up; most of the folks who stuck it out to the bitter end found themselves in dead-end menial jobs in high-security facilities in the middle of nowhere.
With most of the wells shut down and a decreasing amount of investment in security, pirates began using the area as a place to meet and swap goods, with locals turning a blind eye as long as they were paid off. This went on for over a year as the infighting continued at Shiawase Petrochemicals; when one of the administrators for the project discovered
As the place grew, Yamatetsu Biotechnology began playing with their fast-growing architectural coral, and provided the seaweed that is harvested there for food...
The place has a strong tendency to build upward, rather than out, since it’s difficult to establish structures with the sea floor a ways down. The original walkways of the platform have long since been buried by subsequent construction, leaving a lot of the volume of the place dimly lit and humid, leaving most of the place in constant night.
Night City is a mishmosh that evolved from permanent drilling platforms, architectural coral, reused shipping containers, floating platforms towed there as a cheap way to extend the structure, and permanently moored ships that have had the place grow around them. (In the case of spots that got in the way of the architectural coral, this is quite literal!)
Architectural coral is a bioengineered, fast-growing coral designed by Yamatetsu Biotechnology, capable of doing in months (with a little assistance from prefabricated nutrient cores) what usually takes decades. They picked a patch of seamount, anchored a bunch of light concrete frameworks in place, attached nuclei to the frameworks along with big nutrient cores, and started it going. As it spread out, they put down conduits (for sewage, water, electricity, and data), tubes (for people to walk through) and bubbles (for rooms) that the coral grew around; after the tubes were completely enclosed in coral, engineers installed bulkhead doors to partition areas off, pumped out the water, and started installing living arrangements. Bioluminescent algae are pumped through transparent pipes in the ceilings of most areas, providing enough light for people with low-light vision see quite well, and even for unaugmented humans who have had some time for their eyes to adjust. (Treat as Partial Light, like city streets at night.)
The staple food of Night City is a bioengineered seaweed called “soyweed” that produces most all the vitamins and amino acids you need for a balanced diet. It shows up as soyweed salad, fried soyweed, boiled soyweed, steamed soyweed, soyweed jerky, is made into patties for soyweed burgers, gets served with rice as soyweed sushi, and even gets ground into soyweed flour to make seaweed bread so you can have buns for your soyweed burgers.
Natural Vat, Inc. also has an operation there, churning out supplementary material and ever-popular flavorings for the otherwise bland soyweed. There are even a few meat vats for the very well-to-do. They also run the sewage treatment there, converting garbage into fertilizer to help feed the populace.
The name is obviously stolen from a setting for R. Talsorian’s game, Cyberpunk 2020, and the idea from the CP2020 Neo-City Project. For floating cities, check out Oceania— the Atlantis Project. I stole architectural coral from Larry Niven’s A Gift from Earth.
The Hibernia platform is Canada’s largest offshore drilling project and is in 80 m of water. There’s a good list of projects at Offshore Technology. The Complete Offshore Employment Handbook is a good orientation, and mentions rigs resting on the bottom in 600 feet of water.
Take a gander at Reef Balls to see an ancestor to architectural coral technology! The Reef Resource Page has some good information, as does Reef Relief. Looks like coral can go at least 240 feet down; massive corals grow 1/8” to 3/4” in a year, while branching corals can do 8” in a year.