The Mezquita is one of Spain's (and Europe's) finest tourist attractions, and a fascinating reminder of the period of Arab rule over large parts of Southern Europe. Córdoba at that time was a lot bigger than today, and the capital of a large empire stretching well into North Africa. The Mezquita was the major mosque in the western part of the Muslim domain, and one of the largest anywhere. It includes a very big courtyard and is especially famous for its 856 columns. After the reconquest, it was turned into a cathedral, and during the Renaissance, a nave was built in its centre. Today it is a fascinating mixture of Islamic and Christian architecture. The mihrad (prayer niche) especially is still very well preserved, and there are some remains of the Visigothic church of San Vicente, which preceded the mosque.
The Mezquita was inscribed in 1984, and the site was extended in 1994 to include the entire Historic Centre. This is also quite nice, but nothing really special. There is a Roman bridge (at least the foundations are still Roman), a medieval tower on the other end of the bridge with a somewhat tacky museum, a very small synagogue (one of only three or four remaining in Spain), the Judería district with many historic palaces and townhouses, and, as the city's major sight next to the Mezquita, the Alcázar de los Reyes Cristianos, a major palace with beautiful gardens. It was the royal residence where the reconquest of Granada was planned and where Columbus presented his plan for a voyage to India (or America, as it turned out).
The fascinating ruins of Medina Azahara (Madinat al-Zahra) are close by and add an additional facet to the story of Córdoba.