These ruins are 4,000 years old!
For a list try this List of archaeological and artistic sites of Sardinia - Wikipedia
a cool site for more info.sardegnarcheologica.it
and more
And maybe some newer ruins (WWII maybe?)
See this page about Wikiloc | Percorso La Maddalena - Le fortificazioni di Marginetto, Cala Lunga, il Costone e Spalmatore