Cultural site in Naples

Forty metres under the old centre: Greek quarries, Roman aqueducts, and the cisterns the city sheltered in during the bombing. Guided only, about an hour and a half, and one optional passage is narrow enough that it is honestly not for everyone. Cool underground whatever August is doing above.

Early Christian burial galleries cut into the tuff, frescoed from the second century onward, and far roomier than the word catacomb suggests — these are wide corridors rather than crawlspaces. Guided, run by a local cooperative, and easily paired with Capodimonte on the same hill.

The oldest working opera house in Europe, older than La Scala, with a red and gold auditorium that daytime guided tours get you inside. A performance is the better experience where the dates allow. Next to the royal palace and the arcade, so it slots into a walk rather than needing a trip of its own.

Naples' answer to Milan's arcade, built a decade later on a similar scale, directly opposite the opera house. Free, roofed, and a useful shortcut in rain. Worth looking up at the glass and down at the zodiac set into the floor, then moving on.