Which wine is often fortified, comes from Spain, and can vary from dry to sweet?

Sherry is a fortified wine that originates from the Jerez region of Spain. This wine undergoes a unique production process that includes fortification, where a distilled spirit (usually grape brandy) is added to increase the alcohol content and stabilize the wine. Sherry is known for its wide range of styles, which can vary significantly from dry to sweet. The different styles are achieved through various production techniques including the use of biological or oxidative aging processes, allowing for an array of flavor profiles.

In contrast, Port is also a fortified wine, but it specifically comes from Portugal and does not typically encompass the same variety of styles as Sherry. Rioja is a region in Spain known for its high-quality red wines, but it is not a fortified wine, nor does it offer the same range of sweetness. Sauternes, on the other hand, is a sweet wine from the Bordeaux region of France, made from grapes affected by noble rot, but it is not fortified. Thus, Sherry is the only wine in this context that fits all the criteria given in the question.