Okroshka, a Russian soup, is cold and undoubtedly has the oddest-sounding set of ingredients of all these soups, more like a salad than a soup, and yet it works wonderfully well.
The sourovetz is an actively fermenting brew. It needs to be made two weeks in advance, so think ahead if it must be authentic. It is a pain and can be replaced by light beer. Neither sourovetz nor beer should be added to the other ingredients until the soup is ready to serve as the soup is liable to turn.