When Ramon Llull was 30, married with children, he was interrupted in the course of writing a love letter to his mistress by a floating apparition of the crucified Christ. He abandoned his family and set off on a path of profound mysticism and ultimately martyrdom, all based around a rather unique project.
Growing up on Majorca in the 13th century, Llull had been surrounded by Muslims and Jews, and he determined to create a sort of scientific general proof of Christianity in order to convert them. This would be his Art, striving for the absolute highest of human sciences.
Since all three religions agreed on the existence of God, and on His having certain attributes (goodness, greatness, eternity, etc.), and all drew from Greek science and logic, Llull devised a system to map everyone's agreements and orient them to a Christian conclusion. Far be it from me to summarize it further: Frances Yates compared Llull's Art to a "huge unclimbed mountain."
Even just visually, before you get into the content, you've rarely if ever seen anything like it: interlocking proofs, like Medieval computer science or a mandala.