The National Museum of San Martino is housed inside the Certosa di San Martino. It presents evidence of the history of Naples from the Bourbon era to the post-unification period.

From Brundarte - http://www.brundarte.it
The nativity scene section, located in the area where the kitchens of the ancient Certosa were, revolves around the grandiose Cuciniello nativity scene, certainly the most famous eighteenth-century nativity scene in Naples of the type defined as "cultured", also well known abroad. Today it occupies an entire room dedicated to him and is undoubtedly a true masterpiece of Neapolitan nativity scene art.

From Wikipedia - The museum is made up of numerous sections housed in different rooms of the charterhouse, including in the rooms of the Prior's Quarter, in the pharmacy, in the refectory, in the cells of the Carthusians, in the ancient guesthouse or in some rooms on the second floor of the cloister great. The museum sections are: the Carriage Hall, the naval section, the Orilia collection, the Charterhouse Picture Gallery (inside the rooms of the Prior's Quarter, with pictorial and sculptural works already from the ancient picture gallery or in any case coming from the religious complex) , the nativity scene section, the Opera museum (inside the rooms on the ground floor of the large cloister), the section of memories and images of the city (on the ground floor and first floor of the large cloister), the decorated arts section and the theatrical one (both on the first floor of the charterhouse), the Rotondo collection (in the rooms overlooking the internal courtyard) and finally the Prints and Drawings Cabinet (on the first floor of the building)

Foto Di Lalupa - Opera propria, CC BY-SA 3.0, commons.wikimedia.org

The Certosa di San Martino and Castel Sant'elmo dominate Naples from the Vomero hill. From the lookout in front you can enjoy a breathtaking view

Foto Di Pietro Scerrato, CC BY 3.0, commons.wikimedia.org

The Neapolitan Nativity Scene: an ancient tradition that is continued and respected by the artisans of the Neapolitan workshops.

The most famous street, where to find the "Pastori" (The characters of the Neapolitan Nativity Scene) is Via San Gregorio Armeno, in the heart of Naples. Here the artisans pass down from generation to generation the mastery and the most sophisticated techniques to create their terracotta works, modeling the characters down to the smallest details, and dressing them with fine fabrics. The reference is the 18th century Neapolitan Nativity scene, a splendid example of which can be admired in the San Martino Museum.

The characters of the Neapolitan Nativity Scene have an important symbolic value: they sometimes refer to pagan cults prior to Christianity, cults that have deep roots, or they symbolize the virtues and principles of the Christian faith.

Those that cannot be missed in the Neapolitan Nativity scene are these:

Benino

Benino is the sleeping shepherd boy. According to some legends, the Nativity scene was born from his dream and would cease to exist the moment he woke up. This character symbolizes the wait for Christmas, the path that every man takes towards this miraculous event. Also known as the "shepherd of wonder" he is usually positioned under a haystack

The wine seller

The wine seller, or "Oste", symbolizes the Eucharist, and is part of the group of food seller characters, who allegorically represent the twelve months of the year: January: butcher or butcher; February: ricotta and cheese seller; March: chicken seller and seller of other birds; April: egg seller; May: married couple with basket of cherries and fruit; June: baker; July: tomato seller; August: watermelon seller; September: fig seller or sower; October: vintner or hunter; November: chestnut seller; December: fishmonger or fisherman.

Ciccibacco

This funny character is placed in one of the two caves located on the sides of the Nativity. He carries an ox cart and carries barrels of wine. he represents the personification of the pagan god Bacchus. He has a ruddy appearance and a prominent belly. Generally he is accompanied by pipers and flute players, thus recalling the Dionysian rites of antiquity. Ciccibacco, in some way, reminds us how thin the boundary is between sacred and profane.

The fisherman

He is represented with his shirt open on the chest, which represents the people, and his trousers rolled up below the knee, as if he were about to enter the water. Sometimes he carries the fishing rod, sometimes not, but he always has his fish counter, another of the characteristic figures of the Neapolitan nativity scene. He represents life, but also the lower hell, Hades, as opposed to the upper celestial world embodied by the Hunter. But the Fisherman also recalls Saint Peter, the 'fisherman of souls', and in general the symbolism of the fish used at the time of the persecution of Christians to indicate Jesus.

The two companions

the two companions, zi' Vicenenzo and zi' Pascale, drinking and chatting companions, have the appearance of two cheerful and carefree friends. In reality they are the personification of Carnival and Death. In the Fontanelle cemetery in Naples there was a skull called “A Capa 'e zi 'Pascale” to which prophetic powers were attributed, and people asked it for advice on numbers to play in the lottery.

The gypsy

The gypsy, traditionally, is able to predict the future. There are various interpretations of this figure. A legend has it that, having predicted the birth of Jesus and having committed the sin of presumption, she was transformed into an owl. The gypsy with the child in her arms symbolizes the prophecy of the flight into Egypt while without the child she recalls the passion of Christ and the desperation of the Madonna. It is believed that she is heir to the figure of the Cumaean Sibyl.

The Three Wise Men

According to Christian tradition they moved from the east, the starting point of the sun. They were originally represented on the back of three different animals, the horse, the dromedary and the elephant which symbolized Europe, Africa and Asia. Currently, figurines depict them riding camels. They were wise men with royal and priestly powers. The Gospel does not speak of their number, which tradition has set at three, based on their gifts, gold, incense, myrrh, which was then assigned a symbolic meaning.

The Neapolitan Nativity Scene has an ancient history, which dates back to the year 1000!. Even today, in Neapolitan homes, during the Christmas period, families dedicate themselves to creating the nativity scene, with the characters purchased in Via San Gregorio Armeno or with the shepherds inherited from parents or grandparents.
You choose a suitable table or piece of furniture and start by creating the mountains with rock paper, and then position the houses. The most skilled, naturally, try their hand at creating their own little houses, recycling boxes and tins, to decorate with tempera colours.
Moss is used for a more realistic effect; with tinfoil you create the river where the water actually flows, thanks to the accessories that can be bought in Via San Gregorio Armeno.
In the end, the entire family gathers in admiration of their work.

But, to tell the truth, not everyone likes the nativity scene: the famous scene from "Christmas in the Cupiello house" is unforgettable where the great Eduardo De Filippo is busy making his Nativity scene and asks his son: "do you like the Nativity scene?" And he replies "I don't like it!"

A little history - from Wikipedia

The Neapolitan nativity scene is a representation of the birth of Jesus traditionally set in eighteenth-century Naples.

Neapolitan nativity scene art has remained unchanged for centuries, becoming part of the most consolidated and followed Christmas traditions of the city. Famous in Naples, in fact, is the well-known street of nativity scenes (via San Gregorio Armeno) which offers a showcase of all the local craftsmanship relating to the nativity scene. Furthermore, there are numerous city and non-city museums (such as the San Martino museum or the Caserta palace) in which historical pieces or entire scenes set during the birth of Jesus are exhibited.

...  In the seventeenth century the nativity scene expanded its scope. It was no longer just the cave of the Nativity that was represented, but also the external profane world: in pure baroque style, representations of taverns with well-displayed fresh meats and baskets of fruit and vegetables became widespread and the scenes became sumptuous and detailed (Michele Perrone was among the leading artists in this field), while the characters became smaller: wooden or papier-mâché mannequins were also preferred in the eighteenth century.

The golden century of the Neapolitan nativity scene is the eighteenth century, when Charles III of Bourbon reigned. Thanks to the artistic and cultural flourishing in that period, even the shepherds changed their appearance. The clients were no longer just the religious orders, but also the rich and the nobles.

One of the richest and largest collections of nativity scenes in the world can be found in the Bavarian National Museum (Bayerisches Nationalmuseum) in Munich. The majority of the collection came to the museum from the private collection of Max Schmederer.

But the Museum of the Certosa di San Martino is certainly the point of reference for studies on the Neapolitan nativity scene, in addition to the rich nativity scenes still preserved intact in Naples and elsewhere. Perhaps the most famous and acclaimed example of a Neapolitan nativity scene is the Cuciniello nativity scene created between 1887 and 1889 and exhibited in San Martino; another very famous one, sometimes exhibited in the royal palace, is the Banco di Napoli Nativity Scene which also has figurines made in the eighteenth century by Lorenzo Mosca. In the twentieth century this tradition gradually disappeared, but today large nativity scenes are regularly set up in all the main churches of the capital Campania and many Neapolitans still set it up in their homes.