Creating empty real life cites in unreal

Hi there, I’ve been seen a lot of people post videos of them selves walking around cities such as Japan, Italy, Going to Airports where there are no people in the city, I’ve seen some things around on Youtube of people not being able to tell if it’s 3d or not, I was wondering if someone could point me in the ight direction to look into making something like this as it’s amazing and I’m quite curious to know how it’s all done

thank you in advance