Segesta's theatre sits high on Monte Barbaro, with the stage opening to a broad view of western Sicily rather than to a built backdrop. The present structure dates mainly to the Hellenistic period, and the site was later reused through Roman, medieval and Arab phases.
It takes a little more effort to reach than the temple, but the view is the reward. If you only have time for one slow moment at Segesta, sit on the stone tiers and let the landscape do the talking.