Castel Nuovo (Maschio Angioino)

You walk in under a white marble triumphal arch, squeezed between two of the round towers, the Torre di Mezzo and the Torre di Guardia. Alfonso I of Aragon had it built to celebrate his victorious entry into Naples, and it is one of the key works of the Renaissance in the city. Stand back on the piazza to take it in, then look at the contrast with the grey stone towers either side.

The towers tell the castle's story. The Angevin king Charles I started the castle in 1279 and it was finished about three years later. The Aragonese rebuilt it as a modern fortress: four towers are of grey piperno stone and one of yellow tuff, on a base with walkways for the guards. The walls you see largely date from restoration works in the early 20th century, when the city cleared away the buildings that had grown up around it. The arch is free to see from the square even when you skip the ticket.

The city lists this route for the Museo Civico:

• The monumental courtyard, with its low Catalan arcade and an outside staircase in piperno by the Majorcan architect Guillem Sagrera. It gives the corner the look of a Spanish patio.
• The Hall of the Barons (Sala dei Baroni), up that staircase. It was the castle's great hall, and Naples' city council met here until 2006.
• The archaeological route in the former Armoury (Sala dell'Armeria). Excavations found Roman remains from the 1st century BC and the 5th century AD, and you look down at them through a glass floor.
• The Palatine Chapel of Santa Barbara, from the 14th century, the only surviving part of the Angevin castle.
• The Cappella delle Anime del Purgatorio.
• The first-floor picture gallery of the Museo Civico.

The three rooms most likely to be closed for events (Barons, Armoury, Palatine Chapel) are also the three best. If all three are shut, the courtyard and the paintings alone are not worth €10.

Under Robert of Anjou in the 14th century the castle was a centre of culture: the city's own history page lists Giotto, Petrarch and Boccaccio among those who stayed. In December 1294 its great hall saw the abdication of Pope Celestine V, and days later the election of his successor, Boniface VIII. The Aragonese kings made it their residence and turned it into a fortress. Under the Spanish and Austrian viceroys, from 1503 to 1734, it was a purely military site, and under the Bourbons it was hemmed in by warehouses and houses until the 20th-century clearance.

Excavations for the metro station next door uncovered Roman Naples' harbour, with Roman ships, and the castle's outer Aragonese towers are now built into the passage from Molo Beverello to Municipio station. If you are catching a ferry, walk that corridor.

Pay at the desk by card, or buy online on the Comune's ticketing site. Rules worth knowing: no food or drink inside, no drones, and commercial photography needs a permit. Small dogs are allowed on a lead if carried inside the buildings. Groups are capped at 30 people.

Timing: it is open on Wednesdays, when the Palazzo Reale and Capodimonte are both closed, which makes it a good Wednesday plan. It is useless on a Sunday. Go in the morning, when events are less likely to be setting up. Check whether the Campania Artecard fits your plan: at €10 full price, this castle is one of the cards' better savings.

Castel Nuovo sits in the Via Toledo and Municipio area, a short walk from the ferry piers at Molo Beverello for boats to the islands. The Teatro di San Carlo, the Palazzo Reale and Piazza del Plebiscito are all within 10 minutes on foot. A sensible morning is the castle at 9 a.m., the Royal Palace next (not on a Wednesday), and lunch in the Quartieri Spagnoli.