Upvote:-2
Though I am not from Galicia myself I have been there many times and have very good friends in Galicia. They told me once in the area near La Torre de Hercules percebeiros risk their lives to obtain the precious percebes seafood.
When IΒ΄ve read your question it made me guess if maybe this is something conected to the activity of percebeiros to store fishing accesories. You should also bear in mind that legal percebeiros with persmission to fish find the competition of ilegal fishermen. So maybe the cave is used by these. I am just guessing here, have no real answer!
I leave an article from a galician neewspaper where they mention about the fights between legal and illegal percebeiros
Hope this helps Luis