ANACHRONISTIC KABBALAH: A Syndey Morning Herald travel piece on Safed in the Galilee in says the following:

Zefat (also spelled Safed, Szfat, Tzfat and Sfat) is considered the birthplace of Kabbalah and, after Jerusalem, is regarded as Israel's holiest town. Situated in the Upper Galilee, it has been home to some of Kabbalah's greatest mystics during the past 2000 years.

Kabbalah is the study of the mystical aspects of Judaism. And according to rabbis in Zefat, Kabbalah is to the Torah (Jewish bible) what philosophy is to science; in other words, it is the study of the hidden and the spiritual aspects of God's commandments.

The most famous Kabbalist to have a strong connection with Zefat was Rabbi Shimon Bar Yohai, who wrote the Zohar, considered the chief work of Kabbalah. During the second century he spent 13 years living and studying in a cave near Zefat with a group of his students.

The Zohar was at least mostly written (in Shimon Bar Yohai's name) by Moses de León and his circle in Spain in the late thirteenth century.