I have lived in 7 houses, only one didn't have a window and only that one had a fan, all the others we have simply opened that piece of glass in a frame allowing fresh air in and damp air out. Simple.
An open window, is subject to which way the prevalent wind happens to blow, if it blows at the window, then the moist air will be blown into the house, rather than being extracted. An extract fan, always extracts.

