The monastery lies on the west slope of Mt. Helikon, below the acropolis of ancient Steirion. It is enclosed by a wall and comprises two- and three-storeyed blocks of cells, a bell-tower at the SW corner, the Refectory on the south side and the two adjoining churches, at the centre of the enclosure.
The smaller church, dedicated to the Theotocos, was built in the 10th century. It is the earliest known example of the four-column, cross-in-square type, it has a spacious, two-column narthex on the west side and a portico to the west of it. This portico actually connects the two churches. The walls are built in cloisonne masonry and are decorated with rich brick (Cufic) ornaments. The diaconicon and the arched portico between the diaconicon and the pulpit were decorated with beautiful wall paintings slightly later in date (11th-12th century) but traces of earlier frescos have also been revealed.
The famous fresco of Jesus of Navi, discovered in 1965, dates from the 10th century and actually belonged to the facade of this church but was later covered by marble slabs when the wall became an interior wall of the catholicon. The interior of the church is distinguished by the rich sculptured decoration of the templon, the capitals, even the drum of the dome.
The catholicon is the earliest preserved specimen of the octagonal cross-in-square type of church, built in the first half of the 11th century. It has a large, tall cupola with a diameter of 9m. The domed central space is surrounded by two-storeyed constructions which were modelled as cross-vaulted chapels. A two-storeyed narthex was built on the west side. The church was built of large, ancient stone blocks and the external walls are very simple, without brick ornaments.
The walls are veneered with marble slabs on the lower section and decorated with superb mosaics on the upper part and the upper floor. The mosaics represent the more severe and abstracted style of the Middle Byzantine decorative art and date from the first half of the 11th century. The Pantocrator and Archangels in the dome belong to a later phase. The mosaic decoration of the walls was completed by contemporary wall paintings in the chapels of the west side. The marble screen was decorated with icons by Michael Damaskenos, dated to the 16th century.
The catholicon is built over a large crypt, shaped as a cross-in-square church, with groin vaults forming the roof. It is dedicated to Aghia Varvara (St. Barbara) and contains three tombs: the one in the north wall is the tomb of Hossios Loucas. The roof and much of the walls are covered with wall paintings, dated to the first half of the 11th century.
The monastery was founded by the hermit Loucas Stereiotis, who lived in the area from 945 A.D. until the day of his death, in 953 A.D. The church of the Theotocos was built while Loucas was alive. He was declared an Hossios of the Orthodox Church and His relics were cept in the church but were later moved to the crypt below the catholicon when this was built.
The catholicon was damaged by an earthquake in 1593 and its dome collapsed but it was rebuilt. The church of the Theotocos was also damaged by an earthquake in 1790 and was supported in 1848. The monastery again suffered serious damage during bombardments in 1943.
The church of the Theotocos, damaged by an earthquake, was supported as early as 1848. In 1870-71 it was painted and filled with plaster casts which were removed in 1971. The Department of Restorations of the Ministry of Culture started repairs of the catholicon in 1939. The dome was strengthened, the mosaics of the church and narthex were cleaned and the window-frames, which had been broken during the bombardment were replaced. The frescoes of the crypt were cleaned in 1960.