Simulacrum

Write about a huge building in your world. Who built it and why?
The Simulacrum is not just a Building. It would be right to call it a mega structure. It is defenetely one the biggest structures constructed by mankind in the modern era if not the biggest. As a structure its shape is one of a big black sphere. It's exterior surface is dark opaque glass and due to its shielding from UV Light it is impossible to look inside the sphere from outside. Its diameter is circa 50 km and the sphere is floating on ocean surface on the coast of the now completely flooded New York City. All around, the sphere is framed by the colossal buildings of the central part of Simulacra, some of those buildings even go almost as high as the top of the sphere. It's said that the sphere is not attached to anything and could withstand any kind of natural disaster as it was originally imagined as a sort of Arc for mankind salvation. What is certain is it's total energetic independence from the rest of the city since it is electrically fuelled by nuclear fission engines located at the bottom of the sphere, under sea level. It's energetic independence is made necessary to prevent any power shortage to the NETWORK, which is a net of powerful processors which allow the functioning of the Neural Network that governs the city. The construction of such a massive sphere was made possible by the invention, in the late XXI century of the Scanner, which is a new technology based on swarms of nanobots which can be programmed to gather particles of material and build structures like some kind of autogenerative foam. Inside the megastructure live milions of users of Simulacra. Citizens of Simulacra which resides in the Simulacrum tend to reject the concept of labor since they've always been served by intelligent machines, however some of them are occupied by the building and repairing supervision of the sphere or by the upgrading of the code which governs algorithms and artificial intelligence of the network and are called Engineers. Engineers also share the most crypto value of Simulacra shared currency and so are able to collectively govern by majority. Entrance to the Simulacrum is heavily guarded and not permited to anybody. You need to be a Simulacra user and not have any kind of restrictions due to bad social behavior, which is per se a difficult thing to mantain, and you also need to ask for a permission from the NETWORK. Once you are able to enter you cannot freely roam inside the sphere but you are supposed to take the shortest route possible to the place of your business. You cannot talk to or bother the Engineers and you need to have valid IDs when the drones approach you for identification. If you are caught breaking the rules you are immediately thrown off the sphere by the guards (sometimes even in the ocean!) or are incarcereted by the guards waiting for collective judgement. You would never be granted another permission inside the city thou, since crime is already submitted as NFT on the Network Ledger and in unmodifiable.