The cathedral stretches the full width of the Plaza de Armas — a single 100-metre facade of white sillar punctuated by twin bell towers. The current building dates from 1656, but it has burned and been rebuilt after earthquakes so many times that the interior is largely neo-classical from the late 19th century. Inside, the highlights are an enormous Belgian-built organ (one of the largest in South America), a Carrara marble altar, and the silver-and-gold-encrusted trono de la Virgen paraded around the plaza on feast days.
A small museum, accessed from the courtyard at the cathedral's south side, displays liturgical silver and treasures. The rooftop tour climbs a series of stairs onto the roof for an extraordinary view of the plaza and the volcanoes — well worth the small fee.