Brace yourself for this great baroque cavern of Catholicism. The faithful believe that it was here on 2 January AD 40 that Santiago saw the Virgin Mary descend atop a marble pilar (pillar). A chapel was built around the remaining pillar, followed by a series of ever-more-grandiose churches, culminating in the enormous basilica. A lift whisks you most of the way up the north tower from where you climb to a superb viewpoint over the domes and city.

Originally designed in 1681 by Felipe Sánchez y Herrera, the basilica was greatly modified in the 18th century by the heavier hand of Ventura Rodríguez. The exterior is another story altogether, its splendid main dome lording over a flurry of 10 mini-domes, each encased in chunky blue, green, yellow and white tiles, creating a muscular Byzantine effect.

The legendary pilar is hidden in the lateral passage behind the Capilla Santa. A tiny oval-shaped portion is exposed on the chapel's outer west side and a steady stream of people line up to brush lips with its polished and cracked cheek, which even popes have air-kissed. Parents also line up from 1.30pm to 2pm and from 6.30pm to 7.30pm to have their babies blessed next to the Virgin. More than the architecture, these sacred symbols, and the devotion they inspire, are what makes this cathedral special.

Hung from the northeast column of the Capilla Santa are two wickedly slim shells that were lobbed at the church during the civil war. They failed to explode. A miracle, said the faithful; typical Czech munitions, said the more cynical.

The basilica's finest artwork is a 16th-century alabaster altarpiece by Damián Forment. It stands at the outer west wall of the choir. There are also two Goyas. La Adoración del Nombre del Dios is an early classical piece from 1772. Vastly different is Regina Martyrum painted in a cupola above the north aisle in 1780, outside the Sacristía de la Virgen. With its blurry impressionistic figures, it was hugely controversial at the time.