Herculaneum (Ercolano in modern Italian) was a small wealthy Roman seaside town of around 5,000 people on the Bay of Naples when Mount Vesuvius erupted on the afternoon of 24 October AD 79. The same eruption that buried Pompeii under several metres of cool ash buried Herculaneum, fifteen kilometres closer to the volcano, under roughly twenty metres of superheated pyroclastic flow — an avalanche of gas, ash and rock that surged through the streets at around 500°C. The two burial mechanisms preserved different things, and that single fact is why Herculaneum is the more rewarding archaeological visit for most travellers.
Pompeii's ash buried furniture, doors, wooden beams and food, but those organic materials slowly decayed under the cool dry pumice over the centuries. Herculaneum's pyroclastic flow carbonised those same materials almost instantly, turning them into stable charcoal-like forms that have survived the past two thousand years substantially intact. The result is unique: at Herculaneum you walk into Roman rooms with their wooden partition screens still standing on their hinges, see a carbonised wooden bed in the position it was last slept in, and pass a baker's counter where the loaves were still in the oven when the surge arrived.
The excavated area is small — roughly a quarter of Pompeii's open footprint — and the visit takes two to three hours rather than a full day. Houses survive up to three storeys where Pompeii preserves mostly ground floors. The Casa di Nettuno e Anfitrite holds one of the finest in-situ glass-paste mosaics in the Roman world. The Boatsheds along the ancient shoreline contain the skeletal remains of around three hundred citizens who tried to escape by sea, discovered as recently as the 1980s and displayed where they fell. The Villa of the Papyri — partly excavated, largely still buried beneath the modern town — yielded the only intact ancient library to survive antiquity, now being decoded by modern X-ray and AI techniques.