If you want a truly unique travel adventure, I would suggest you go to San Diego and visit one or all of the 7 caves there.

And for the most enjoyable part, you can have the chance to see La Jolla Caves through kayak.

Here's a good article for you:
You Gotta See La Jolla Caves

And here's a list of videos you can watch and see how people go about it.
La Jolla Caves Videos