Naples Archaelogical museum.

There is a manned left luggage at Naples' Central station: https://goo.gl/nqrPpK
Don't know what are you exactly afraid of as you're going to take the metro during the day, but in Naples the rule is: no jewels, no rolex... no problems.
Follow red signs to Garibaldi M1. Take a train headed to Piscinola and get off after stops 5 at a station called Museum (what else?).
If you want to see the famous art stations of Naples M1 metro, I think the most praised one today is Toledo, but you can google image it and decide by yourself.
Relax, you're going to Naples, not Beirut.

It's not me, it's my other half. We routinely leave most jewelry and valuables at home, and we'll use the under clothes pouches that day for the rest. I personally think Naples sounds like fun and if we do it this day we have an entire day in sorrento to do whatever we want. Thanks. I'll pass on your info.

We did this on our way from Amalfi to Rome...I had no qualms leaving my bags at the main train station. Well - there is always that niggling thought - but I would make sure anything of great value - like an ipad or a laptop - was buried in the middle of the bag (or on your person). Don't leave anything of worry in the outside zippers. This is the livelihood of these people, so I think if they were getting a bad rep for stuff going missing, they wouldn't last too long. We've also left bags at the Pompeii stop, in London, Pisa and other places. If you are carrying a larger day bag, you may have to leave it in the lockers at the museum.

We took the subway to the museum and back - depending on how much of a hurry you are in, it seems like it could be a long walk...

The Deposito Bagagli is in the train station near the police station, just be sure of opening/closing times. I drop my carryon at the station when I am just passing through Napoli so I can dash out for a walk and a pizza.

I'd be more worried about someone grabbing the luggage from me in the train station than while it's in storage. Not that I was particularly worried about it, but I was solo and had a rather long wait for my train . . . and had undoubtedly been psyched out by stories about "Naples."

PS - there are clear instructions in the RS books about getting from the station to the museum. Allow enough time to see the museum properly. I think 2 hours is less than the bare minimum.

Everyone has their own style of travel. We had to spend a night in Naples because our cut-rate flight from Stanstead arrived so late. That gave us time to visit a bit of Naples and check into our Sorrento hotel around 4PM.

If you are staying in Sorrento to facilitate day trips, why not see the museum on a day you are going "that way" on the train to see Pompeii or Herculaneum? Alas, the "one-day" train pass has been eliminated, so you will need a ticket for each journey. But the whole point of staying in the pleasant but unremarkable Sorrento is convenient day travel. Related issues are the weather that day, and your hotel's distance from the Circumvesuviana station. (i.e. we walked a mile to the Naples rail station to improve our survey of the city.) Don't miss the Farnese Marbles in the same museum.

I would hope transit crowding is less of a problem in April. We were there late may, and the Circumvesuviana was jam-packed, even without rush-hour.

We had no issues walking around Naples, but be very vigilant as a pedestrian. The chance of muggings is much over played; the odds of being hit in a crosswalk by cars that don't pay attention to the rules strikes me as high. We felt we were taking our lives in our hands trying to cross the road.

I don't understand why everyone is so skittish about Naples. With "Breaking Bad"s basis in fact, and heroin usage in wealthy U.S. suburbs exploding, it's unreasonable to fear a city with more dense history than even Rome. Maybe it's because some posters here have never read Rick's general advice about a belt-safe money pouch for ALL OVER Europe. I would avoid driving into Naples, just like I would avoid driving anywhere near Los Angeles. The only difference between the Circumvesuviana and the London Underground at rush hour is the accordions. And I've seen my share of Mariachi guitar groups on the NYC subway!

Enroute to Sorrento in July of 2013 my sisters, niece and I spent half a day in Naples. We cked our bags at the train station and had no problems. Kept our passports with us. Very easy to take the metro to the arch. museum. From there we followed the R.S. walk down Via Toledo to the Castel Nuovo & back up Toledo to the Spaccanapoli stopping for the ricotta filled pastry, sfogliatella, along the way. Loved ckg out the shops here selling presepi. We had pizza at Pizzeria Trianon (right nearby is Piazzeria Michele from the Eat Pray Love movie.) We never felt threatened or afraid & we had a great afternoon. The only bummer was the mosaics collections rm at arch museum was closed that day. Not enough people wkg that day to staff it we were told. So 3 months later I go back with with my husband who had not been to the museum either & not only was the mosaics rm closed but a bunch of others too according to a sign they post near the tkt office. We just bagged the museum then.