Citara's defining fact is that it is a thermal beach on an active volcano, and the clearest expression of that is the Giardini Poseidon Terme, the thermal park that occupies the southern arc of the bay.

The source is the volcano. Ischia is not a sedimentary island with incidental hot springs; it is a volcanic complex that rises roughly 900 meters from the sea floor in the northwest of the Gulf of Naples. Its central peak, Monte Epomeo at 787 meters, was lifted by block resurgence of a caldera formed in the Monte Epomeo Green Tuff eruption about 55,000 years ago — the tuff colored green by chlorite, an iron-bearing phyllosilicate. The island's last eruption, the Arso flow, occurred in 1302 AD and lasted around two months. Ischia is still volcanically active, and that activity surfaces as fumaroles, low-energy seismicity, and hot springs. At Citara, that last expression — thermal water — reaches the shoreline. The dark, lithic sand underfoot is the same story written at grain scale: GloPrSM modeling puts the sand at roughly 69 percent lithic, the signature of a volcanic terrane rather than the calcareous sand common across the Mediterranean.

The park that the water built. In 1959 a German physician, Gernot Walde, looked at the Citara bay — then farmland running down to the beach — and built the first developed thermal garden on Ischia. He cut a series of pools into the slope, linked them with paths, and named the complex for Poseidon. In the 1970s the Bavarian industrialist Ludwig Kuttner took it over and, with the architect Fritz Zollinger, redesigned it into the terraced park that exists now: more than twenty thermal pools running from 28 to 40 degrees Celsius, three seawater pools, and a steam cave cut directly into the volcanic tuff in the Greco-Roman manner. It is the oldest and largest thermal park on the island, and it is the reason most people know the name Citara at all.

The bay faces the sunset. Citara opens to the southwest, across the Tyrrhenian toward Procida and the Phlegrean Fields. That orientation is not incidental to its reputation — it is why the bay is one of Ischia's established sunset locations, and why the whitewashed Chiesa del Soccorso, on its promontory a short walk into Forio, became the island's signature place to watch the light go down over open water. The church itself, rebuilt in 1864 over a 14th-century convent foundation, holds votive ship models left by shipwreck survivors, a reminder that this is a working seafaring coast and not a resort invention.

The honest tension. The same volcanic system that warms Citara's water is the system that shakes Ischia. The island sits on active faults; the Casamicciola earthquake of 1883 killed roughly 2,300 people, and a magnitude-4.0 quake on 21 August 2017 killed two and left around 2,600 homeless, both on the north coast. Citara is not the epicenter of that danger, but it is fed by the same geology. The beach is a place to sit in mineral water warmed by a living volcano — which is exactly what makes it worth describing precisely rather than loosely.