Like many other Byzantine monasteries, Osios Loukas Monastery is situated in a picturesque valley with olive trees on the slopes of Mount Helicon - opposite Mount Parnassus. The monastic complex is in harmony with the surrounding landscape, following the example of the ancient temples.

The buildings are considered being the largest and best preserved of the Middle Byzantine period, with extraordinary architecture and excellent decorations of mosaics, frescoes and sculptures. The complex is enclosed by a wall and comprises blocks of cells, a bell-tower, the refectory nowadays a museum - and two churches.

The katholikon - main church of the monastery - was built in 1011-12. This cathedral is the only surviving structure to have eight pillars surrounding the central dome. The second one is the Church of Theotokos (Virgin Mary). This is the only church in Greece that is certain to have been built in the 10th century. The architectural design of the church follows the typical Byzantine architecture of "cross-in square" type and the walls have been built out of a mixture of bricks, marble and stone. It became the prototype for all the classical Byzantine churches of southern Greece.

The monastery was founded around the middle of the 10th by the monk Loukás (St. Luke). His relics are exhibited in the katholikon. They were stolen by the Crusaders during the 13th century and kept in the Vatican for centuries.

The monastery of Osios Loukas - still inhabited by monks - is included in the list of world heritage monuments of UNESCO.