The residence is a great place if you want to avoid the crowded, noisy larger towns in Sicily and relax in a more peaceful location. From the flat it takes about 25-30 minutes to walk to the beach, closer to a smaller beach and the centre. I highly recommend, because the flat is large, equipped and does not heat up during the day. If you want to visit the nearby reserves, towns and attractions - I recommend a car, there are buses to Palermo or other places, but at the weekend there are not many of them. Some roads were closed, so it was difficult to get from the train station to the centre. Do not trust google maps - they are not updated.
But to sum up, I was in Residence in Castellamare for a month, the place is quiet, great to rest, good location to visit bigger cities such as Palermo Trapani. I would also add that the internet is good - I worked remotely and usually there were no problems. The host is always willing to help, we did not miss anything.