From the 8th century BC until the 7th century AD, this remote twin cove was the site of the ancient city of Karthaia, one of Kea's four historic city-states. Now the partly uncovered ruins sit in splendid isolation, only accessible by boat or on foot. Three hiking trails lead here, with the easiest being route 6: a 40-minute walk down from the parking area at the bottom of a narrow lane, signposted from the main road at Stavroudaki.
Part of the great charm of this site is that you'd be very unlucky to find more than a handful of people here – and there's a good chance you'll have it completely to yourself. The small, craggy acropolis has the remains of the Temple of Apollo Pythios on its lower level and the Temple of Athena at the top, dating from 530 to 500 BC. Down below is a theatre that once seated 880 people, and the remains of a Roman-era bathhouse.