Wow, at first I thought that this would be a discussion of a cave that looks just like this just off of one of the beaches of Santa Cruz Island off the coast of California. It is part of the Channel Islands. It is accessible by kayak or swimming. I wish I had the waterproof digital camera that I have now, then I could have something to post to support this.

The Island also has one of the longest sea caves, it goes back almost a mile, and if the tide is right can be explored with kayaks.