Ancient Karthea in Kea lies on the southeastern coast of the island, surrounded by hills, valleys, and the Aegean Sea. It functioned as a powerful city-state from the 8th century BC until the 6th century AD. 

The ancient city stretches across two main terraces within a large fortified area. First, on the upper terrace, the Temple of Athena stands with its Doric columns and sculpted marble remains. Built around 500 BC, it once honored the goddess of wisdom and war. Today, many of its carved stones, including scenes of Amazon battles, sit inside the Archaeological Museum of Kea.

Next, on the lower terrace, the Temple of Pythion Apollo dominates the sacred zone. This structure dates back to 530 BC and served as the spiritual heart of Karthea. A monumental gateway, built in the 5th century BC, marks the entry to the temple grounds. 

In addition to the temples, Karthea includes several other important structures. A processional road, paved with stone, links the two terraces. Along this path, Building D showcases a columned entrance and a mosaic floor from around 300 BC. Moreover, the theater nearby once seated around 1,000 spectators. Roman baths also appear closer to the valley of Vathypotamos, offering a glimpse into daily life during the later period of the city.

Access to Ancient Karthea requires effort. Most visitors hike from the village of Stavroudas. The downhill path stretches 1.7 kilometers and takes about 45 minutes. The return hike, uphill, often lasts up to 90 minutes. For an easier trip back, some locals offer donkey rides. Others choose to arrive by boat. The site remains open to the public year round and entrance is free of charge. Also, there is a small beach close to the site for those who want to combine their visit with a swim.

Because the site remains remote, visitors should come prepared. The area offers no shops, cafés, or restrooms. Therefore, bringing water, food, sun protection, and proper footwear is essential. Mobile reception fades in several areas, so planning ahead ensures safety.

In conclusion, Ancient Karthea blends rich history with striking natural beauty. The journey requires effort, yet the reward is timeless.