We visited the castle with a guide for the full price of 16 euros. You must make a reservation online before your visit. The place was nice and interesting. The full pass gives you access to the top terrace of the castle from where you can see the whole city of Napoli. The museum was also interesting

Don't bother. Even when there is no line you have to buy a ticket online! No tickets at the entrance. 6€ self walk only gets you into what used to be the Kings Room. €16 is a guided tour in under 40 mins. This place is run down and not looked after. The Kings room is now used by their local government as a working office. They don't respect the history here, everything is covered in rubbish, scaffolding or power points and cables.

Incredible castle with a nice view on Naples The guide was so nice, interesting and fried friendly. The guide allow how to go down in the cell. Surely unavoidable while going to Naples. A audio guide or Qr code with app that allow us to get some explanation on the painting in the museum. The reservation system that can be tricky: you need to actually book a time slot before you got the entrance ticket.