Ask HN: How do large private infrastructure projects get started?

I'm curious to learn more about how large, private, high upfront investment projects get started and built. For example, sports stadiums, cinemas and concert halls/theaters, ice rinks and public swimming pools.

I understand some amount are started by the city, region or country itself. What about the private ones? And what are the differences between Europe and the US in that regard?

Bit of a long shot question but it's difficult to even know what to look for to learn about this. If you know that field I'd love to talk to you directly!