This is a very convenient way to go up the hill to Vomero. It will take you to Piazza Fuga in Vomero. From there it will take about 10 mininutes to walk to Castel Sant'Elmo (or Certosa e Museo di San Martino further downhill). Bear in mind that signs are practically non-existent when you get off the funicular in Vomero. So count on an unintended "scenic" tour as you get lost in the neighborhood.
This funicular is one of four in Naples and takes the strain of walking up and down some serious hills. Cheap to use and works most of the time, occasionally out of service so be prepared.
They had strike 9.9.2024, but you couldn't see that and machines for buying tickets still worked. We bought 5 daily tickets for metro that doesn't work at all.