Complex sentence: They set out to a number of underwater archaeological sites and finally arrived at Cape Gelidonya, where they spent most of their time trying to identify the site, but finally on the last day located the site on one of the small islands off the Cape.
Split into simpler sentences: They set out to visit a number of underwater archaeological sites and finally arrived at Cape Gelidonya, where they spent most of their time trying to identify the site. Finally on the last day they located the site on one of the small islands off the Cape.