If you expect to find anything like the Córdoba mosque on a hill/mountain top in the Sierra de Aracena, you deserve the disappointment you will certainly feel. Just enjoy this remarkable building for what it is. The bases of the columns go back to Roman times, after which there was a Visigoth church here. It was then transformed into a mosque and fortified to take advantage of its situation -- this is what mainly stands there now. It has Moorish arches between its five naves [again not ornate like the ones at Córdoba or Medina Azahara.
Immediately adjacent is a 19th-century bull ring, which I believe is still used once a year. This is all FREE.