On August 17, 1826, Prussian poet August Kopisch, painter Ernesto Fries, local sailor Angelo Ferraro, innkeeper Giuseppe Pagano, and donkey-driver Michele Federico defied Capri legends of sea demons to explore a "cursed cave." Christening it the Blue Grotto, Kopisch rejected the name "Grotta Glauca" suggested by Russian exile Apostol Mouravieff, and published his account of the discovery in 1838. Located on the north-western coast of Capri, in the municipality of Anacapri, this karst cavity originally served as a prestigious maritime nymphaeum for the Roman emperor Tiberius, acting as a submerged annex to the overlying Villa of Gradola. Following centuries of decline—during which it appeared on Vincenzo Coronelli's 1696 map merely as "Gradola"—European fame arrived with Wilhelm Waiblinger's 1828 writings and Hans Christian Andersen’s 1835 novel *The Improvisatore*. These literary works transformed Capri from what writer Daniello Bartoli called a "Cliff of the Desperate" into a prominent Grand Tour destination.
What to see
Visitors enter the main cavern, known as the Duomo Azzurro (Blue Cathedral), an erosion cavity measuring 60 meters long, 25 meters wide, and 22 meters deep, with a vaulted ceiling averaging 7 meters but reaching 14 meters at its highest point. Including the submerged threshold, the total vertical space is 36 meters. The intense blue illumination is created by an underwater window located precisely beneath the entrance; this natural filter absorbs red light and allows only blue to pass through. Objects submerged in the water take on a silvery glow due to air bubbles adhering to their surfaces, altering the light's refractive index. Toward the back, tunnels branch off to the left, while the right side features a cavity shaped by condensation and thermal shifts. The south-western corner holds a Roman platform leveled using crushed brick rubble (*signino*). From here, the Galleria dei Pilastri splits into three branches leading to the Sala dei Nomi, named for the signatures left by 19th and 20th-century travelers. The accessible area ends at the Sala della Corrosione. Historically, the walls were lined with Roman statues, confirming its use as a nymphaeum as intuited by archaeologist Amedeo Maiuri. Figures of Poseidon and a triton, recovered during 1963 excavations, are now displayed at the Museo della Casa Rossa in Anacapri.
Visiting
Entry depends entirely on sea conditions. The opening is a narrow cleft in the rock, two meters high and two meters wide, sitting just one meter above the waterline when the sea is relatively calm. To pass through, passengers must lie flat in small boats while an expert boatman temporarily abandons the oars, pulling the vessel inside using an iron chain anchored into the entrance wall. The tour halts at the Sala della Corrosione; the passages beyond, dug in vain by the Romans in search of fresh water, possess unbreathable air and cannot be explored.
Our editors' tip
To witness the full effect of the blue light, the sea must not be perfectly flat. Due to the physics of total internal reflection, the underwater threshold requires at least a slight movement in the water to successfully illuminate the cavern.