How to get rid of the smell of mustiness from a summer cottage?

The smell of mustiness is a specific and often unpleasant odor that can appear in various places and situations. It is associated with the presence of mold or fungi, which thrive in damp, poorly ventilated, or damaged rooms. This problem often occurs in old tenement houses or summer cottages, for example, which are not heated. How to get rid of this smell? If we remove the cause, will proper ventilation be enough? Are there any special products that can help? Do we need to replace the furniture because this smell may have sunk in? How to protect a summer cottage for the autumn/winter period so that the situation does not repeat itself every year?