Port is like any other wine in that it needs to be stored in a cool (55-65 degrees or 12.5-18 Celsius) and a dark place where the humidity is kept between 60-75%. A temperature controlled wine cellar is ideal for this, but a cool “passive” cellar or inside closet will also work. So long as the temperature does not get too warm in the summer you are typically in good shape. Heat is the enemy of wine in general and even though Port is more hearty than most, if it gets too hot, it will damage your Port and impart off flavors. Also try to avoid direct sunlight or fluorescent light, as well as vibrations which have a negative effect on long terms storage of Port wine.