Córdoba was once the most populous city on earth, where art, science, and trade prospered and three religions lived together in (tenuous) peace. That was the 10th century; before that, the Romans and the Visigoths left their marks and since then the Spanish Christians (including the Inquisition) have also added to the incredible mix of history in this city.
It was fun to explore the sprawling old town, discover little squares and churches, and hang out along the old Roman bridge in the evening. This is also where I first experienced the real Andalusian Holy Week festivities (Semana Santa). Of course, to see these ominous costumes firsthand was a bit jarring at first as they so closely resemble the Ku Klux Klan's. But the Spanish version is much older and apparently came about as a way for Christians to show penitence to God but not to other people (hence the anonymity of the hoods). It was fascinating to witness.