On January 23, 1938, speleologist Franco Anelli descended into a 60-meter-deep abyss, revealing a 3,348-meter-long karst system that began forming 90 to 100 million years ago. During the Upper Cretaceous, present-day Apulia was submerged beneath a sea teeming with mollusks, whose organic remains compressed into a massive sedimentary layer known as the Limestone of Altamura. When the landmass emerged 65 million years ago, the rigid rock fractured extensively. Rain and river water infiltrated these fissures, carving out an underground canyon aquifer that reaches a maximum depth of 122 meters. Following an aborted 18th-century expedition led by local Vincenzo Longo, Anelli finally mapped the complex at the invitation of the Bari Tourist Board, assisted by local worker Vito Matarrese. The exploration of the site remains an open chapter: a 2006 cleanup project that cleared river and infrastructure debris from the main abyss revealed evidence pointing to still-undiscovered underground corridors.
What to see
The system begins with the Grave, the only cavern communicating directly with the outside world. This colossal sinkhole—100 meters long, 50 meters wide, and 60 meters deep—is illuminated by a natural skylight ringed with holm-oaks. A single sunbeam strikes the "Cyclopes," a group of stalagmites resembling sea giants, while the southern walls and moss-grown columns remain in permanent darkness. Moving deeper, visitors enter the Black Cavern, its walls darkened by the endemic fungus Scolecobasidium anellii, and the Cave of the Monuments, an expanse so vast that Anelli's acetylene lamp could not pierce its gloom. The route passes highly specific formations: the Stocking (a stalactite shaped like women's tights), the Owl, the Snake Corridor, and the sheer drop of the Precipice Cavern. The extended route continues into the Desert Corridor, an underground Grand Canyon entirely devoid of concretions and tinted red by iron minerals. Beyond the Leaning Tower of Pisa cavern—featuring a slanted stalagmite beside a small drip-water lake—and the Dome cavern, lies the system's climax. Discovered in 1940 by Matarrese, 1,500 meters from the entrance, the White Cave is accessed through a small portal dug into alabaster. Inside, two immense columns support a vault surrounded by dazzling white, translucent stalagmites and coral concretions, prompting Italian President Luigi Einaudi to declare it "the most beautiful in the world" in 1952. The caves also host a highly specialized isolated ecosystem, including the endemic pseudoscorpion Hadoblothrus gigas, the isopod Murgeoniscus anellii, and five species of bats.
Visiting
The caves maintain a steady temperature of 18 °C and are open year-round, excluding Christmas Day and New Year's Day. Two routes are available: a 1-kilometer base path lasting 50 minutes, and a 3-kilometer full itinerary taking two hours. The summer season also includes guided night tours. Elevators and stairs now provide access to the Grave, replacing the original rope descent. Above ground, the Franco Anelli Speleological Museum operates in a 1952 building designed by architect Pietro Favia. Inaugurated in 2000 and managed by the local speleological association Gruppo Puglia Grotte (founded in 1971), it houses a documentation center and a 3D multimedia room opened on December 9, 2015. The site is directly served by the Grotte di Castellana railway station on the FSE line.
Our editors' tip
Look closely for the "bacon slices"—layers of alabaster so thin they become translucent when lit from behind. Also, pay attention to the eccentric stalactites, which defy gravity by growing horizontally or in curved patterns. This phenomenon occurs because their central cannula is less than a millimeter wide, forcing the calcite to crystallize outward, influenced by air drafts and mineral impurities in the water.