https://en.wikipedia.org/wiki/The_Line,_Saudi_Arabia
"The Line (stylised THE LINE; Arabic: ذا لاين) is a conceptual linear smart city in Saudi Arabia in Neom, Tabuk Province, housed in a single building, that is designed to have no cars, streets or carbon emissions.[2][3] The original plans called for the city to span 170 kilometres (110 mi) at a height of 500 m (1,600 ft)[4] and a width of 200 metres (660 ft) sized to accommodate a population of 9 million"
My personal pet dream, if i had a sufficient number of billions, - several large, like that Wright's, skyscrapers 30+ km into the ocean off the SF Ocean Beach (the depth there is like 50-80m, so sub-1M tons of concrete and steel would give you a 100m-side square foundation with 10m walls, and such foundation itself already can house 10-20 underwater stories)