I have explored and photographed the ruins just off Lungomare Dante Alighieri, near the division between Trapani and Erice, on several occasions over recent years.
There is a fence around the ruins but, I noted today, that part of a wall that used to be boarded up has been destroyed since my last visit.
The fence on the bay overlooking Trapani has been knocked down so it's easy to enter the site. Judging by the quantity of broken beer, wine and whisky bottles I presume that the site is used at night for illicit parties or as a place to sleep for the homeless.
The site itself was once the Tonnara San Giuliano, one of several tuna canning factories along this stretch of coast. I am not sure when or how it fell into ruin but it seems there are plans (slowly developing ones!) to build an hotel on the site.
On the Trapani side of the site the beach runs in a long curve to the opposite side of the bay. In summer the beaches are crowded but there are places to get drinks, snacks or meals. Car parking is always an issue.
On the Erice side the sea laps close on rocky outcrops that extend to the road near the Grande Migliore store - about 150 metres - and from there the sandy beach extends to the old windmills at San Cusumano.
I decided to get more photos of the site before it disappears, though there is a good chance the place will remain as it is for a couple more years!
Worth exploring if you happen to be in the area and especially if you like nature - there are a few species of birds to see, and wild flowers.