Apano Kastro or Palaiokastro or Tis Phaneromenis
Also built in a strategic location north of cove Korthi by Venetian Marino Dandolo during his rule, it was the second strongest castle-town of Andros, after Mesa Kastro of Hora. It was built in a naturally fortified spot, at 600 meters above sea level.
There is little information about the history of Pano Kastro, especially about the conditions under which it was abandoned. In any case, the castle must have been abandoned by the 19th century. Legends and traditions are quick to fill in the gaps of history: it is said that the Turks used an elderly woman and her pregnant daughter in order to conquer the castle. Asking for help, they were accepted inside the castle and at night the old woman opened the gates. The Turks entered and slaughter the entire population. Plagued by remorse, the woman hurled herself from a cliff and the beach was named after her "Tis Grias to Pidima" (“Old Lady's Leap").
Today, in the area of Palaiokastro, there are only a few remnants of houses, of the wall and of the church of Koimisi tis Theotokou (Mother Mary’s Dormition) or Phaneromeni. But the view to the Aegean is nothing short of spectacular.

Location / Access
It is located over village Kohylou, 9 km from cove Korthi. There is a dirt road after the village and then a path with stairs all the way to the top, where the Castle is located, dominating the scenery.

Days / Hours of Operation
Free access

Mpisti-Mouvela Tower
Owning a Tower, a fortified mansion, survived as a practice in Andros up to the 19th century as a relic of feudalism, despite the social reforms. After the departure of the Venetians and the annexation of Andros to the Ottoman empire, the feudal system was preserved, by which the Venetian ruler governed a whole area and had tenant farmers to cultivate his land. 
The Towers were the fortified residents of feudal rulers, built away from the sea in carefully selected locations in their estates. The oldest references to this Tower are by explorer Tournefort in 1700, who mentions it as "the Tower of the Aga".
The tower of ruler Mpisti (today owned by the family Mouvela) is one of the oldest preserved towers of Andros, its three storeys dominating the hill and overlooking the whole area.
The huge gate was of solid wood and had an opening at the height of the first floor. Access to that level was achieved by a wooden ladder that was retrieved at night. After the danger of pirates waned, a stone ladder was built. For the Tower’s defense, small openings were made in the walls, from which boiling oil was dropped. On calmer times, the big lounge had a capacity of 300 guests! Today the tower of Mpisti is abandoned.

Location / Access
At the edge of settlement Stenies.

Days / Hours of Operation
Access is free but visitors must be careful because the tower is abandoned and requires urgent renovation.

Tower of Agios Petros (saint Peter)
A cylindrical, 20 meters high, stone edifice of the Hellenistic age (3rd century b.C.) with five storeys and a domed roof. Its strategic location enabled it to be used as an observation post. Inhabitants would be warned with smoke signals that pirates were approaching and prepared accordingly.

Location / Access
It is located 3 km northeast of Gavrio near the village bearing the same name. From the central road we approach the monument either by the dirt road or on foot.

Days / Hours of Operation
Free access at all times

Venetian Castle or Mesa Kastro
After Frankish rule is established in Cyclades, Andros is given to Marino Dandolo, nephew of the Doge of Venice in 1207. To protect the island from pirate raids, Dandolo builds on the eastern side of the island a central fort, which was to become the military and administrative center of the island, replacing the Byzantine center Mesaria.
In the rock’s perimeter stood a rectangular wall with towers, a water basin and Dandolo’s palace, all built with local, grey rock. A stone, single-arched bridge connected the Castle with the mainland, probably replacing a mobile one. In the narrow, rocky end of the peninsula, outside the castle, the town was developed, the medieval settlement of Kato Kastro, today’s Hora.
Mesa Kastro must have been very well preserved until the 17th century, despite being abandoned and is mentioned by many travelers who were impressed by its structure and stone bridge. After the bombardment of Hora by Germans in 1943, only a few ruins and the bridge remained, until that, too, was destroyed by a natural disaster in 1952. It was rebuilt with the same techniques and materials.

Location / Access
It is located in Hora, at the end of the peninsula.

Days / Hours of Operation
Access is free. The more daring can cross the narrow bridge and approach more; most, however, admire it from the square of "Afanous Nafti".