There is another ruins here in Trafalgar. These ones are Phoenitians, that came to Spain any hundreds years before the Romans. It is a temple that later was offered to the goddess June. And later was destroyed by the arabs to obtein stone to build a castle against the Spanish Reconquest.
You can see the morter, like a cement made with lime and sand. It is still working.
And that could be a bathroom, I think that is impermeable.