San Blas is made up of over 160 islands there! If you're looking for a place where there is a scrap of sand, a palm tree and nothing else - this is the place. In San Blas, there are limited places to stay - on an island, the place usually has rooms and serves you three meals a day (usually lobster!)!
If you're a vegetarian or don't do sea food, it is somewhat limited - try and get in touch with the hotel beforehand although be warned, this usually doesn't mean you'll get anything different!!
San Blas is where the Kuna Yala people of Panama are based - trying their hardest to be autonomous from main land panama - with their own language, currency and governance. On some islands you'll see women selling traditional crafts, usually the fabrics with embroidered designs - molas. Really great for souvenirs!
Most hotels have a boat service as part of what you pay a night - to take you to the various islands. They usually take you to another island, drop you for a few hours, come back for you, take you to another and then back to the island you are staying!
There is a museum based on one island - it is more really a house with some preserved items inside but worth the visit - certainly to find out more about the indigenous people there.
If you want to escape to a place where you just island hop, swim and read your book, this is the place :)