Tucked at the base of the dramatic limestone cliffs of Capo Caccia near Alghero, Neptune’s Grotto is one of Europe’s most celebrated marine cave complexes. Formed around two million years ago, the cave opens into a series of vast underground chambers filled with massive stalactites, stalagmites, saltwater lakes, and towering calcite columns. The geographic quirk making this cavern unique is its direct opening onto the open sea. Because of this, boat access is entirely dependent on sea and wind conditions: even a gentle swell from the west makes docking impossible, leaving visitors to descend the famous Escala del Cabirol, a panoramic staircase of 654 steps carved into the sheer cliff face.