So you're visiting Pompeii or Herculaneum, and the whole time you're thinking - Sure, these buildings are great, and these plaster body casts are amazing, but what happened to all of these people’s stuff? The answer is The National Archeological Museum of Naples.
Wandering through the upper levels of the museum offers up-close views of some of the most well-preserved examples of Roman art. Enjoy intricate mosaics, including portraits, a massive and breath-taking battle scene featuring Alexander the Great, and a "Cave Canem" sign (the ancient equivalent of the "Beware of Dog" sign on the gate to your back yard). The faun statue from Pompeii's House of the Faun is also there, perfectly preserved (sorry, that was a modern replica you saw at the site). Wander through cases of ancient jewelry, admiring the tiny, hand-carved details.
And--the juiciest bit of all--visit the museum's notorious "Secret Cabinet." When Pompeii was first excavated, archeologists and the clergy alike were horrified by the abundance of sexual imagery and objects they found. In an effort to conceal the Romans’ dirty little secret, many of the objects--ranging from sculpture to fresco to bronze work - were removed and placed in an off-limits section of the museum. For years, most people didn't know the room existed and those who did had to apply for special permission to see the pieces. Now, the room is open to the public, though the museum still isn't bragging about it or publicizing it much (it still isn‘t mentioned on the museum's website). The items range from the piously religious (small sculptures of reproductive organs used as offerings by those who hoped to conceive) to the genuinely beautiful (an amazing fresco of the Three Graces) to the genuinely raunchy (most of which probably isn't appropriate to mention here). In ancient Rome, however, sexuality was viewed as both a highly sacred and a highly amusing part of life, and if the Secret Cabinet establishes anything (once you get over the initial shock), it is that very dramatic difference between the ancient Romans and society today.
The museum houses ancient sculpture not related to the sites destroyed by Vesuvius, but with the exception of a few select pieces (for example, the Farnese Bull), the real draw is the artifacts. They provide not the images of emperors and gods that you will see in most other museums, but instead let you look into the lives of average people, and that rare perspective is what makes the museum so unique.