The monasteries and chapels that spreads around the island, number more than 350! When you climb to the Castle of Guerini you will find two churches. St. George’s Glykafli, built in 1790 with wooden temple and the Lady of the Castle (Annunciation), built in the mid 18th century woodcut iconostasis, dressed with gold leaf and a sculpture-headed eagle on the floor.

In Chora, the church of Panagia Portaitissa constitutes the religious centre of the island and the most renowned and visited spot of worship. It started being built in 1762 by Saint Anthimos from Kefalonia, who, despite the fact that he was blind, had previously built the monasteries of Zoodochos Pigi at Sikinos and of Saint George in Kastellorizo. The construction of the church lasted for nine years and, during those years, a plethora of miracles are said to have happened according to religious tradition.  
The church is dedicated to Panagia Portaitissa of the Holy Monastery of Iviron. A copy of the icon of Panagia Portaitissa of this monastery at Mount Athos was brought to Astypalaia by Saint Anthimos.

Also, in Chora you will find Megali Panaghia church with its pebbled courtyard. This is part of a complex of five churches which, with the sea as their background, create an enchanting picture.

It is worth visiting the Castle of Agios Ioannis in the southwest coast of Astypalaia, that dates back to the Byzantine times. The construction of the castle coincides with the period of time when piracy was flourishing in the Aegean Sea. The construction of fortresses in locations that were far from the sea or up on hills, was a common measure of protection of the population from the raids of pirates and other enemies. The location of the castle of Agios Ioannis can confirm the aforementioned theory. It was built on the highest spot of the island, above the large homonymous beach which is only accessible by boat or on foot by following the mountain route.

Panaghia Flevariotissa Monastery is the most beloved church for the residents of Astypalaia. On February 2 each year, the feast of the Presentation of Christ is the most important festival of the island. It is a whitewashed church surrounded by additional auxiliary buildings as well. Tradition says that in a small cave next to the church was once a shepherd of the icon who moved to town and returned the next day saw the cave again. The story was repeated until it was decided to build the monastery.

Very known is the church of Panaghia Poulariani that lies NE on the way to Vathy. She is the patron of sailors. The rock here is in the shape of the Virgin with child in her embrace. According to tradition, during bad weather the lights come on. The church can be reached by boat or by footpath.

Among the island there are also many churches scattered as that of St. Nicholas on the hill near Deep Inside, the church of Our Lady of Thomas and St. John. Agios Dimitrios, the church of the Ascension in Maltesana, Saint Nicholas, Saint Basil, Saint Panteleimon, St. Eleutherius, St. George and St. Constantine.