We only had one full day in Napoli so instead of doing the full day trip to Vesuvius/Pompeii, we decided to just stay in Naples and see what the city had to offer. One of the things that popped up in our research was Napoli Sotterranea, which is a series of underground tunnels and caves, used as a bomb shelter during WWII. It's about 130 feet below ground and 280 miles long. There are various access points, but all require a tour, which makes sense because how would you even navigate 280 miles worth of a cave?
We reserved our tickets online for €14 with Napoli Sotterranea - LAES. It's just a reservation so you still need to pay/pick up your tickets in person on the day of. I believe in person tickets were €10 or €11 but you may run the risk of not being able to get a ticket. We did the Saturday 10 AM English tour and it was a pretty big group. The tour lasts for an hour and was very interesting. There are areas of the cave where it's a tight squeeze - you have to walk sideways. But if you're claustrophobic, there is an alternative route for those parts.
Overall, it was a good tour and I'd recommend it if you are looking for activities in Naples. read more