The main tower and a secondary tower of Nuraghe Oes contain a single room, which was once divided into three spaces with wooden garrets supported by recesses, attached thanks to holes made in the walls.
Dating back to a period between the Bronze Age and the Iron Age (9th-6th century BC), the Oes is a majestic work of Nuragic architecture, built using well-finished basalt rocks. The main building consists of a tower (keep) with three floors and a truncated cone shape that ‘falls’ on all sides with a uniform slope. It is made up of 29 rows of stones. It is 16 metres tall and has a diameter of 11 and a half metres, making it the largest Nuragic building found so far. It once had a tholos vault (false dome). Against it, there is a bilobed bastion, with a perimeter of 50 metres, on two levels and with two entrances, that encloses a courtyard and two secondary towers. One of these is well-preserved. The overall complex measures 425 square metres and also includes a sacred area, with a fence (temenos) that has a vaguely hexagonal shape and a little megaron temple, the remains of a Tomb of Giants, of which you will notice the stele resting on the ground, a vast residential settlement of circular and oval huts. Their type is uncertain (perhaps cisterns and a second little temple). Between the sacred area and the Nuraghe, twenty rocks laid on edge and fixed in the ground resemble a megalithic circle.References:
First record of Kastelholma (or Kastelholm) castle is from the year 1388 in the contract of Queen Margaret I of Denmark, where a large portion of the inheritance of Bo Jonsson Grip was given to the queen. The heyday of the castle was in the 15th and 16th centuries when it was administrated by Danish and Swedish kings and stewards of the realms. Kastelhoma was expanded and enhanced several times.
In the end of 16th century castle was owned by the previous queen Catherine Jagellon (Stenbock), an enemy of the King of Sweden Eric XIV. King Eric conquered Kastelholma in 1599 and all defending officers were taken to Turku and executed. The castle was damaged under the siege and it took 30 years to renovate it.
In 1634 Åland was joined with the County of Åbo and Björneborg and Kastelholma lost its administrative status.