Castel Sant'Elmo is a medieval fortress located on a hilltop near the Certosa di San Martino, overlooking Naples, Italy. The name "Sant'Elmo" derives from a former 10th-century church, Sant'Erasmo, shortened to "Ermo" and, finally altered to "Elmo". It presently serves as a museum, exhibition hall, and offices.
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Lago di Agnano or Lake Agnano was a circular lake, some 6½ km in circumference, which occupied the crater of the extinct volcano of Agnano 8 km west of Naples, Italy. It was apparently not formed until the Middle Ages, as it is not mentioned by ancient writers; it was drained in 1870.
The Macellum of Pozzuoli was the macellum or market building of the Roman colony of Puteoli, now known as Pozzuoli. When first excavated in the 18th century, the discovery of a statue of Serapis led to the building being misidentified as the city's serapeum or Temple of Serapis.
https://en.wikipedia.org/wiki/Macellum_of_Pozzuoli
Cumae (Ancient Greek: Κύμη (Kumē) or Κύμαι (Kumai) or Κύμα (Kuma); Italian: Cuma) was an ancient Greek city on the coast of the Tyrrhenian Sea in Campania, Italy. Cumae was the first Greek colony on the mainland of Italy and the seat of the Cumaean Sibyl. It was the Cumaean alphabet that was adopted in Italy, first adopted and modified by the Etruscans (800–100 BC) and then by the Romans (300–100 BC), thus becoming the Latin alphabet, the world's most widely used phonemic script. The Cumaean alphabet was also used throughout the Greek island of Euboea.
Baiae (in modern Italian Baia), a frazione of the comune of Bacoli in the Campania region of Italy, was a Roman seaside resort on the Bay of Naples. It was said to have been named after Baius, who was supposedly buried there. Baiae was for several hundred years a fashionable resort, especially towards the end of the Roman Republic. Baiae was even more popular than Pompeii, Herculaneum, and Capri with the super-rich, notorious for the hedonistic temptations on offer, and for rumours of scandal and corruption.
Sam and companions spend two days on the island of Ischia while the Quaker City remained in quarantine at Naples, from August 7 to August 9, 1867. Mark Twain Project: Quaker City Itinerary
Museo Civico
The Blue Grotto (Italian: Grotta Azzurra) is a noted sea cave on the coast of the island of Capri, Italy. Sunlight, passing through an underwater cavity and shining through the seawater, creates a blue reflection that illuminates the cavern.
https://en.wikipedia.org/wiki/Blue_Grotto_(Capri)
August 10, 1867, Sam and companions visited the Island of Capri by chartered steamer. Mark Twain Project: Quaker City Itinerary