The Great Mosque of Cordoba is the single most important building in the city and one of the most extraordinary in Europe. Begun in 785 by Abd al-Rahman I and expanded across two centuries, it is a forest of red-and-white striped horseshoe arches — around 850 columns of jasper, onyx, marble and granite, many salvaged from Roman and Visigothic sites. The mihrab at the southern end is a masterpiece of Byzantine-influenced gold mosaic.
After the Christian conquest in 1236 the building was consecrated as a cathedral, and in the 16th century a full Renaissance nave was built straight into the middle of the prayer hall. The combination is jarring and unforgettable. Enter from the orange-tree courtyard (Patio de los Naranjos). Free entry weekday mornings before opening hours; otherwise tickets around €13.