Playa Ventanas is one of the best all-around beaches in all of Costa Rica, and it is my personal favorite. A couple of years ago I strapped a GoPro camera on my head and recorded my journey from the front of one of the caves, all the way through, and out on the other side.
CAUTION: DO NOT TRY THIS! IT IS VERY DANGEROUS! I made the video so it is not necessary for you, your guests or friends, to do it themselves.
The caves at Playa Ventanas are the inspiration for the name of the beach itself. 'Ventanas' means 'window' in Spanish. Therefore, these are not caves, these are 'windows' of the beach.
The windows (or caves) at Playa Ventanas are equally beautiful and fascinating. As the tide rises, and more water is forced into the holes of the caves, the louder the WHOOSH!! BANG!! gets, caused by the accelerating water.