We took the funicular to get up the hill and it took a while to find the entrance of the first wall around the castle as it was not clearly marked. When we walk through the port we saw the castle and wanted to walk to it but did not realize see the ticket office (again it was not marked clearly) but one person of the staff pointed us to the right direction. After getting the ticket is was still a climb up to get to the top of the castle. When we were on the top, the view over Naples is astounding. It was worth the climb up to the top. Specially if the weather is good you can see the Vesuvius behind Naples. The castle it self has been maintained very well and it is very clean and neatly. Only the toilets can be improved.
The museum in the castle is in my opinion not worth the visit, but it depends if you like modern art.