The fantastic Castellana Caves (Grotte di Castellana) is one of the largest cave systems in Italy, stretching for over two miles, with many areas still unexplored. The underground tunnels are a natural marvel not to be missed in Puglia, full of strange and stunning geological formations illuminated in a rainbow of colors as the sun moves through the sky.

The only cave of this speleological complex connecting with the outside is the massive La Grave, which is 330 feet long, 170 feet wide, and 200 feet deep. La Grave creates a huge natural pantheon with its opening that lets the sunlight pass through, creating a magical effect where the light moves differently according to the time of the day and the season. The light first illuminates the walls, then the stalagmites, and finally the irregular ground of the cave floor.

La Grave, and the entire cave system, probably originated about a hundred million years ago when the land that now forms Apulia began emerging from the sea. The new land was too rigid and fractures formed, with water infiltrating the soil and slowly creating larger and larger cavities. Gradually the thickness of the rock that separated the cave from the outside became so reduced that the opening we can see now was formed, letting the sunlight illuminate the cave for the first time.

Another beautiful feature of this cave system is the White Cave, made of white alabaster and adorned with crystals and numerous stalagmites, with two big columns that seem to support the whole cave. Throughout the cave system, some eccentric stalactites can be found, growing horizontally or with a curved pattern, instead of the vertical direction they usually assume. The origin of this feature is still debated but one of the hypothesis says it may be caused by impurities in the water.