This historical monastery is the most significant pilgrimage of Tilos and one of the most important reverence points in the Dodecanese. It is located at a height of 270m on the slope of the hill Kryallos, 7 km west of Megalo Horio. Built between 1470 and 1480 and with a fortified architecture it is surrounded by a powerful stone enclosure with a three-storey defensive tower on its southeast end. Its church is in cruciform type with a dome. Dating back to the late 15th century, it met two renovation phases in 1703 and in 1912 respectively. The older hagiographies are located in the nave, where a 15th century representation of the monastery founder, the monk Ionas, stands out. Furthermore, worth noted are its wooden iconostasis of 1714, the wall paintings of Pantokrator on the dome and the Holy Trinity on the apse, works of the painter Grigorios of Symi since 1776.
In the enclosure the legendary cypress that the abbot of the monastery Ieremias planted in 1800 dominates, while other grand trees, plane trees and walnut trees lay their thick shadow over the surrounding area. In 1824 the northern section of the monastery cells was renovated and in 1843 the coating of the courtyard with a mosaic masterpiece of Rhodian style took place.