Capo Caccia never ceases to surprise us and it does so with this splendid cave called Tunnel which crosses from side to side an isthmus which also extends below the surface of the sea. One end of the Tunnel is on the side of the submarine's rock, while the other is on the side that faces north towards the Cabirol stairway which leads to the Neptune Caves. The peculiarity of this cave lies in the presence of an important deposit of very white sand which with the sunlight creates plays of luminous refractions which also affect the inside of the tunnel, in fact entering from the northern side, at a certain point of the route, reached a fork on the right, we can continue straight and by turning off the torch we will observe the sunlight reflected from the bottom of very white sand that illuminates the walls. Rich in Parazoanthus axinellae, it reserves unexpected encounters for the most attentive observers. On the southern side it is easy to find placid groupers.