Panagia Kastriani is the guardian of Kea. It is an imposing monastery (18th century), located on the top of a rock on Kastri hill, which offers magnificient sea and land views. There are two ways to get there. One starts from Ioulida and the other from Otzias.

The monastery was built at this site because there was found the icon of Virgin Mary (Panagia). Some local shepherds were seeing something that shined on the hill and decided to find out what it was. This is how they discoverd the icon which was shining. The locals believed that Virgin Mary "indicated" them that this was the site where she wanted her monastery to be built. Therefore they started buliding the monastery with a lot of difficulties because the spot is remote and stiff.

The monastery has two churches and a guest house which accomodates visitors at a symbolic rent. There is also a dining room and some other rooms which all can be used by guests. The new church is dated from 1910. The icon of Virgin Mary is found inside the monastery.

The Monastery celebrates on the 15th of August and a great fest is held then.