Museo Nazionale Ferroviario di Pietrarsa

The Museo Nazionale Ferroviario di Pietrarsa occupies the former Reale Opificio Borbonico, a royal engineering works squeezed between the Naples-Salerno railway and the sea at Via Pietrarsa 15A, on the edge of Naples where the city runs into Portici and San Giorgio a Cremano. The site covers 36,000 square metres and holds over 55 pieces of heritage rolling stock, with botanical gardens between the halls and the water. Run by Fondazione FS Italiane, it is one of the largest railway museums in the world by area - and it is built on the ground where Italian railways started.

Italy's first railway line, from Naples to Portici, was inaugurated on 3 October 1839 and ran along this shore. The royal decree to buy the Pietrarsa land followed in 1840, on a site that had previously carried a Napoleonic coastal artillery battery. Ferdinand II of Bourbon founded the works to build steam engines and locomotive boilers and to free the Kingdom of the Two Sicilies from British and French technical supremacy; by the middle of the nineteenth century it had become the largest industrial plant in Italy, employing around 1,100 workers. Production ran from 1842 until 1975, when the works closed as obsolete in the age of diesel and electric traction. The museum was inaugurated on 7 October 1989.

The collection is arranged through the original pavilions, each of which once had its own place in the production cycle. Pavilion A holds 26 steam locomotives and four three-phase electric locomotives. Pavilions B and C hold passenger carriages, among them the royal carriage built for the wedding of Umberto II in 1944. Pavilion D is given to diesel locomotives and railcars. Pavilion G, put up in 1840 and the oldest structure on the site, holds models and memorabilia.

The setting does most of the work. The museum sits directly on the shore of the Bay of Naples with Vesuvius behind it and the Naples-Salerno line running along its landward edge, which means you can frame preserved equipment, live Trenitalia traffic, the sea and an active volcano within a short walk of each other. Late afternoon light comes off the water and onto the pavilion facades.

Inside, Pavilion A is the frame that sells the place: 26 steam locomotives ranked in a nineteenth-century industrial hall, with the roof structure of the original Bourbon workshop overhead. The halls are working buildings rather than designed galleries, so light is uneven and mixed - worth a fast lens. Pavilion G, built in 1840, is the oldest structure on the site and the one that most looks its age.

The gardens between the buildings and the sea give you options no indoor museum has: equipment and architecture with palms, open sky and the Gulf behind. If you arrive on the Pietrarsa Express heritage train from Naples rather than by car, the arrival itself is a photograph.

The name to look for is Bayard - the locomotive that hauled the inaugural train on the Naples to Portici line in October 1839, and the twin of Vesuvio. What stands at Pietrarsa is the replica built in 1939 for the centenary of that line, and the museum presents it through a virtual and augmented-reality experience sold as a €1 supplement on the entrance ticket.

Twenty-six steam locomotives under a single roof in Pavilion A is a concentration few museums in Europe can match, and the four three-phase electric locomotives beside them document an electrification system Italy pursued further than anyone else. The carriages in Pavilions B and C include the royal carriage built for Umberto II's wedding in 1944 - the last years of the Italian monarchy, preserved in upholstery and marquetry.

The buildings are the other half of the argument. These are not exhibition halls built to look industrial; they are the actual Bourbon workshops where the Kingdom of the Two Sicilies tried to build its own locomotives, standing where a Napoleonic gun battery had been, with the Naples-Salerno line running past the gate and the Bay of Naples on the far side. Few railway museums put you between live railway traffic, an active volcano and the Mediterranean at the same time.

The museum opens Tuesday to Sunday from 9:30 to 18:00. Plan two to three hours: four main pavilions, a fifth in the oldest building, and gardens running down towards the sea that are worth walking rather than crossing. The site is large and mostly flat, and much of the movement between pavilions is outdoors, so it reads more like a works than like a gallery.

Admission is €9 full and €6 reduced for ages 6 to 17 and over-65s, with under-6s and disabled visitors with a companion free. A guided tour costs €11 full and €8 reduced, and you can upgrade an unguided ticket for €2 at the museum. There are two standing promotions worth knowing: Thursdays drop the price to €5 full and €4 reduced, and the Saturday "Arlecchino" offer covers two adults and two children aged 6 to 17 for €15. Ordinary family tickets are €20 for two adults and one child and €25 for two adults and two children. A Pietrarsa Card season ticket costs €20 for adults.

Check the calendar before travelling: the museum publishes fixed annual closures on 1 to 3 September and 6 October. And note the Bayard virtual reality experience carries a €1 supplement rather than being included.