Situated in the centre of the island, at the site of the ancient city-state by the same name, the capital of Kea, Ioulis or Chora, is a very picturesque town with ceramic-tile roofed houses, cobbled streets, arched passages, steps and squares. Many paths start from Chora and leads to many Historical sites of the island.

At the end of the main stone road of Ioulis or Chora, the capital of Kea, on an old stone road, lies the Lion of Kea. The Lion of Kea, or Lionda, is one of the most famous sights on the island and is an archaic structure carved out of stone. According to mythology, Kea was once known as the Water Island and was given the name Ydroussa. The island was considered to be inhabited by water Nymphs. Due to its exceptional beauty, the Gods were jealous of the island and sent a lion down to ravage it of its beauty. The lion drove all the Nymphs out of the island and the island dried out.

The inhabitants of Kea then asked Apollon’s son, Aristaeus for help and he built a temple to the mightiest of all Gods, Zeus. This act pleased Zeus and he brought rain to the island and the nymphs back to it, as well. The most interesting feature of the Stone Lion is the fact that it has a smiling expression on its face. This adds to the mystery of the statue and its existence, considering that its creator is unknown.

The Archaeological Museum of Kea is found close to the entrance of Ioulida which leads to the central Square. The building was constructed in 1970 and houses findings from all the excavated sites of the island. Findings come from the four ancient towns of Kea: Ioulis, Karthea, Korissia, and Poiessa, that flourished a lot in antiquity and quickly developed strong political institutions.

The collections are divided into two categories, the pre-historic collection and the Historic collection where visitors can see parts of the ancient temple of Athena and particularly parts of the pediment with scenes from the fight of Amazons. Also, there are ceramic vases, marble statues, ancient coins, and columns. Parts of sculptures and buildings can also be found on display on both floors.

There is also a section dedicated to the 19th-century local scholar Konstantinos Manthos (1826-1890), whose valuable manuscripts give a vivid view of life on Kea about two centuries ago and refer to the antiquities around the island.

Ancient Karthea was the most important of the four city-states of Kea in the antiquity. It is located in a region that is pretty hard to access, on the southeastern side of the island, right above the bay of Poles.

Ancient Karthea was founded in the archaic times and its lifespan reached till the early Byzantine period. The route is very popular for trekking on the island, as this site is located about 23 km from Ioulida, the capital of Kea, and then 30 more minutes on foot. A small part of the ancient town of Karthea remains today. The city was surrounded by walls from the archaic and the classical times with at least 6 entrances and towers to protect the area. The city had an extensive defense mechanism which included many towers. Also, it had public buildings, laboratories, mines, water supply system, and its own authorities and laws.

Some of the most interesting monuments in Karthea include the Doric temple of goddess Athena (late 6th century BC) and the archaic Temple of Pythion Apollo (530 BC). In the valley of Vathipotamos, the Temple of Demetra (3rd century BC) along with a theatre (1st century BC) were also discovered. The Archeological Museum of Kea exhibits parts of the Temple of Athena and other parts of this ancient city.

The Monastery of Panagia Kastriani is located on the northern side of the island, 12 km from Ioulida, the capital of Kea. It is constructed on the location Kastri, which is why the monastery was named Kastriani. According to the local tradition, at around 1700 AD, few shepherds saw a light on top of Kastri hill and when they climbed up, they dug and found an icon of the Virgin Mary. On this spot, they built a small church that survives till today. In 1912, a larger church was also constructed that is the katholikon of the monastery till nowadays.

In the premises of the monastery, there is also a two-storey building with guest houses, cells, and auxiliary rooms. At the entrance of the monastery, which is colored in blue and white, there is a tall bell tower. The Monastery of Kastriani celebrates on August 15th. Its location offers a breathtaking view to the Aegean Sea and the island of Andros.

The area of Agia Irini in Kea hosts an ancient seaside settlement that dates back to the late Neolithic Age (approximately 3,300 BC). The first settlement in this hilly area showed that Kea had cultural interactions with continental Greece.

The settlement was characterized by rocky elevations constructed overlooking the sea. The cemetery of the settlement was found at the foot of the hill. It was believed that the inhabitants of Agia Eirini were farmers and fishermen and that they were dealing with metallurgy.

The settlement of Agia Irini also gives indications that the Cycladic culture of the Early Bronze Age existed in this area during the period from 3,000 BC to 1,500 BC. From 1,700 BC and onwards, Agia Eirini town acted as a communication channel between the Minoan and the Mycenaean culture. The geographical location of the island and the availability of a safe harbor contributed to the social and economic development in the area.

The site at Agia Irini is not open to the public. It is protected by a fence and entry is allowed only to archaeologists, after given permission. The tourists are only allowed to walk around the fence and get just a view of the settlement. The site contains plenty of ruins from different ages. The ruins of an old ship can also be seen at the bay close to the site.