A wine cellar is a storage room for wine in bottles or barrels, or more rarely in carboys, amphorae or plastic containers. Wine cellars are usually located completely underground, and often have direct contact to the surrounding soil via a gap in the foundations.

Residential wine cellars can be either active or passively cooled. Actively cooled wine cellars are highly insulated and need to be properly constructed. These types of wine cellars utilize specific wine cellar conditioning and cooling systems to maintain the desired temperature and humidity. Many systems only control the temperature and not the humidity so it is important to look for a system that actively controls both with temperature and humidification integrated into the unit. Passively cooled wine cellars take advantage of naturally cool and damp areas (such as basements with uninsulated outside walls in cool and temperate climates) when minor seasonal and diurnal temperature variations can be tolerated. Passive wine cellars may be less predictable, but cost nothing to operate and aren't affected by power outages.

*source: wikipedia