This large cave, with scattered Taíno pictograms (and graffiti) and stalactite and stalagmite formations, is several kilometers west of Boca de Yuma on the way toward the entrance of Parque Nacional Cotubanamá.
There is normally a caretaker sitting outside the entrance who can accompany you up the rickety ladder and deep into the cave (a small gratuity is appreciated). To find the cave, follow the paved road that runs along the ocean wall west (away from the mouth of the river); you need no more than 15 minutes inside.