1. Naples Underground or Napoli Sotterranea is a fascinating subterranean space that offers visitors a glimpse into the history of Naples. It is a labyrinth of tunnels, cisterns, and chambers that have been excavated over the centuries under the city. The underground complex is believed to date back to the Greco-Roman period and was subsequently used as a quarry, a refuge during World War II, and for various other purposes.

Some interesting highlights of the Naples Underground include:

- The impressive Greco-Roman aqueduct that once supplied water to the city

- An ancient Greek theater that was rediscovered in the 1970s

- A medieval market that was used for trading goods until the 19th century

- A WWII air-raid shelter that provided refuge for thousands of Neapolitans

2. The working times of Naples Underground can vary depending on the season, but generally, it is open from 10 am to 5 pm every day. It is closed on Tuesdays. The phone number for Naples Underground is +39 081 296944.

3. The ticket prices for Naples Underground start at €10 for adults and €8 for students and younger visitors (aged 4-18). There are also family and group tickets available. Visitors can purchase tickets online in advance or at the entrance to the underground complex. Naples Underground is located in the historic center of Naples, close to Piazza Cavour, and can be reached by public transportation, such as the metro or bus.