Andre from Quebec forgot his bathroom fan. Now what to do?
Well Andre, it is true that a charcoal recirculation fan will pick up and deal with most odours in the bathroom, if you keep the filter changed. But it will have absolutely no affect on moisture build-up, and hence on the possible development of mould or mildew.
Although many building codes in this country allow an operable window as a ventilation system, I don't think that anyone who has allowed that in the code ever tried to open, or at least tried to close that open window in the middle of January. It simply freezes up. We need exhaust fans in bathrooms. But you actually have a lot of choices Andre.
You apparently want to avoid the traditional large square box cut into the ceiling with ductwork out the side wall of the attic or out the roof (never out at or under the soffits). You could put a very discrete little round grill in the ceiling or even the top of a wall which connects to an in-line fan. This kind of fan allows you to put the motor anywhere, my choice is in the basement, by sneaking the piping through a hollow wall, or down the backside of a closet that butts onto the bathroom. Check out the keyword "Exhaust Fans" for many more options.