Pablo and Julia (14) kiss each other and it's implied she does something to his genitals which happens off-camera (we only see him pull up his trunks right after). Next we have Gonzalo is in bed masturbating under the sheets, with flashes of his experience with the girl in his mind, mixed with visions of Paco (the 'stranger').
Near the end of the film Benno is seen frontal nude from a distance, he stands on the edge of an indoor swimming pool and fires a pistol. Plus mainly rear nudity when he's swimming afterwards.