Chagigah חגיגה

All are obliged to appear before God at the three festivals, except those the tractate names one by one: the deaf, the minor, the one who cannot go up on his own feet. Then come the festival offerings, their measure and order, and the purity in which people went up to Jerusalem.

The second chapter suddenly changes subject: "one does not expound the forbidden relations before three, nor the work of Creation before two, nor the Chariot before one, unless he is wise and understands of himself." The Gemara on this passage tells of the four who entered the orchard, of whom only Rabbi Akiva came out whole. This is the headwater of all Jewish mysticism.

Order: Moed. There is Gemara in both the Babylonian and the Jerusalem Talmud.