The Monastery of St. John the Theologian, set like a crown on top of the settlement of Chora, is the island's landmark. Its construction started in 1088, when the Byzantine emperor Alexios Comnenus the First granted the whole island to St. Christodoulos to organise a settlement for monastic purposes.

He named the monastery and its fortress after the Evangelist John, who had written the book of Revelation on Patmos almost a thousand years before. By the 13th century the villagers, many of whom were descendants of the original builders and craftsmen of the complex and who were initially ordered to live far away from the monastery, were allowed to settle around it, not only to seek refuge from the pirates inside, but also to defend it.

The monastery is constructed on five levels, is surrounded by impressive 15 meter walls and overlooks the whole island. The whole complex has, beside the monks' cells around the main church called catholicon, ten more chapels and an exquisite museum with century-old religious objects, paintings and manuscripts.

Halfway on the hill between Skala and Chora lies the Apocalypse Cave, where St. John the Evangelist wrote, according to tradition, the book of Revelation when in exile by emperor Domitianus. It was in this sacred cave where on one Sunday in his very old age John heard the voice of God and received the command to write about everything that was to be revealed to him.

During his initial vision, where the Lord appeared to him in all His Glory amidst seven golden lanterns, the enormous solid rock that formed the roof of the cage was divided in three parts, and this huge crack symbolising the Holly Trinity can be seen today in the grotto, along with the spot where the evangelist used to rest his head while sleeping or taking a break from dictating the revelations to his student Prochorus.

The visitor enters after going down forty-three steps, and the atmosphere is awe-inspiring and filled with mysticism.