According to the Bible, John was sent to the island of Patmos and there he had a vision. According to lore, this occured in a cave while John dictated his vision to a scribe. This fresco, over the entrance to the cave building depicts the scene.

Pictures are not allowed inside the cave, some are posted on other web sites, take the links page to find them. The room is less a cave than a cleft in the rock. Now it is normal room height. Tours go there every day and some worship is held there.