Admire one-of-a-kind 12th, 16th, and 19th C frescoes. Then tour the Sacristy which is a museum – artifacts include the 11thC mosaic icon of St. Nicholas, the actual Chryssobull issued to Ossios Christodoulos and the 6thC Purple Codex of the Gospel of Mark with purple parchment, and gold and silver text. There’s an Art Restoration Workshop as well, and a Library.