At Pompeii there are a couple of places that are included in the ticket but are a short walk away from the main site. I think the House of the Mysteries is one of them. I didn’t do those when I visited but now I wish I had. The National Archeological Museum in Naples has a lot of items recovered from Pompeii and Herculaneum. It’s very interesting and well worth a visit, as is the city of Naples itself. A good outing if you have a rainy day.