The Sassi in Matera is one of the most beautiful and surprising places I've ever been to.
To stay in a hotel like San Giorgio is a unique and amazing experience, which is hard to describe: you sleep in a cave (which, against all expectation, is super confortable), have an amazing breakfast in the room, and walk around at any moment (sunrise or sunset), allowing yourself to get lost and to discover the city once and again.
I can't recommend the experience enough.