Superficial karst complex located less than a mile West from the town of Zugarramurdi (Pamplona, Navarra). The main cavity was pierced by a stream, which still runs through it, for this reason it is called the Regata del Infierno (the Regatta of Hell). The stream is responsible for its shape, that of a large tunnel that reaches a length of 120 meters and a width of 22-26 meters at its eastern end, about 12 meters on its western end, and has an average height of 10-12 meters. There are also two upper galleries, with a similar orientation than the main gallery, to which they open.