Made by rural dairy farmers in the Asturias region of Spain, Cabrales is aged in natural limestone caves from two to six months. During this time, penicillium molds go to work and create complex blue-greenish veins throughout the center of the cheese. This cheese is far more interesting and more worth buying than its better known compatriot, Manchego.
UPDATE: Some cheesemongers describe the flavor of Cabrales as the "meanest" among blue cheeses. Although this is a very enjoyable cheese to eat, I have to confess that I understand what they mean. It is not easy to eat a lot of this cheese in one sitting.