For the casual tourist, while not necessarily the largest cathedral, the Duomo di Santa Maria Assunta, aka Duomo di Napoli, aka Cattedrale di San Gennaro--still presents a visual feast for the eyes. For the spiritual visitor, this cathedral is the city's central catholic parish, seat of the Naples archdiocese, dedicated to the city's principal patron saint.
San Gennaro (Saint Januarius)*, was a bishop martyred in 305 AD under Roman emperor Diocletian, later buried here. While little is known about his life, his body was transferred a few times, lastly in 1497 to Naples. This was at the behest of Cardinal Oliviero Carafa, where his remains were kept in the Succorpo, a richly decorated crypt constructed for this specific purpose.
The most notable religious relics housed here include:
1) ampoules of the saint's blood that supposedly liquify three times a year in a miracle to show the favor of the saint upon the city, and popes that visit. For this reason it's become a pilgrimage site for those hoping to witness the miracle of liquefaction. It's debated what type of liquid is contained within the hermetically sealed vials, though scientific evidence is scant considering the contents cannot be removed in fear of damage to its contents.
2) the treasure of San Gennaro (for which a separate ticket must be purchased €13) consists of the many works bestowed upon or donated to the cathedral over seven centuries from royalty and lay persons, as signs of devotion. Paintings, busts, ex-votos, objects made with precious metals and jewels are included in this collection.
While there are a few sections of the cathedral that are currently not open regularly to the public, including a) the Santa Restituta, where the Baptistery of San Giovanni in Fonte is located (part of the church built earlier in the 14th century--you could peak in from the side though couldn't enter), b) the Chapel of the San Gennaro Treasury, c) the Minuto Chapel, --the parts the were open were very impressive. In the cathedral, highlights include the colorful soaring dome, golden coffered ceilings, and the decorative statue "Assumption" at the main altarpiece by Pietro Bacci (1739). Mid-afternoon lighting thru the windows cast a bright warm glow making the statue look like it was shining. The Succorpo was also one of the most ornate crypts I've ever seen.
Open daily 9:30am-17:00pm, general admission is free and there are tours available with advance booking required (€10 adult, €8 student, €6 6-15yr olds, €0 for 5 and under and those with disabilities.) Tickets for rooftop access are €6. Good-sized gift shop.
For more info - their website is very informative about the duomo's history and visiting details:
https://duomonapoli.it/en/
*This is the same saint for which an annual festival Feast of San Gennaro is held. read more