It has been documented that there is a group of righteous people called "The Nistarim". I am not referring to the lammed vav tzaddikim of the Gemara (Sanhedrin 97b, Sukkah 45b). Rather, a mystical brotherhood whereby the leader goes by the name Baal Shem (see here for wiki article and here for chabad article).
My question is twofold:
What practices did/does this group engage in?
Although all the info I could gather online seems to suggest this group formed around the time of the emergence of Hassidut, I have been told by a particular Chassidic Rebbe that his tradition is that this group dates back to the times of Rabbi Akiva, and the purpose of their continued efforts is to bring back prophecy to the Jewish people through meditative techniques passed down from generation to generation, dating back to Talmudic times, in an attempt to usher in the Messianic era. Does anyone know of any material on this subject?