Well worth a visit (take a picnic), on a par with the Archaeological Park. It doesn't seem to attract a large number of visitors which makes it rather more atmospheric. There is virtually no interpretive information, Iweinvanaalst below has given a detailed description which you may want to read before you go.
To get there catch AST Bus 25, after about 20 minutes there is a stop outside the castle but if you miss that get off at Belvedere which is just a 5 minute walk up the road. The ticket office is down the lane way by the restaurant. Tickets are 4 euro pp.
If you own or manage Castello Eurialo, register now for free tools to enhance your listing, attract new reviews, and respond to reviewers.