The Feast of the Epiphany - January 6
The Feast of the Epiphany has been an important celebration in the Eastern Church for nearly two millennia. From the Greek word epiphanes, the earliest Christian usage of the term comes to us from Clement of Alexandria, who wrote that the Basilideans (a heretical gnostic sect in Egypt), celebrated "the baptism of Jesus" on January 6 (the Feast of the Epiphany). A later reference comes to us from the Emperor Julian (the Apostate) (361).
It is believed by most scholars that Christians, in general, as early as the second century, as well as some heretical groups (noted above), celebrated the "baptism of Jesus by John the Baptist" on January 6. As the Gospels relate to us, it was at this time - "Jesus's baptism" - that the Holy Trinity was manifested in unity, with the Holy Spirit descending like a dove out of the sky, the thundering voice of the Father proclaiming, This is my beloved Son in whom I am well pleased (Matt 3:16-17). And the "manifestation" of the "Son [of God]" (v. 3:17) as the Messiah at the beginning of His ministry.
As time progressed, the Feast of the Epiphany became a conflation of numerous celebrations, including the Feast of the Nativity (Christmas - which continues to be held on January 6 in the Russian Orthodox Church). Also, the stories of the "Wedding at Cana" and the "Feeding of the Five Thousand" have come to be celebrated on January 6 (probably as a polemic against the Greek god Dionysius, or Bacchus).
In later centuries, especially in the coastal villages of Greece, the practice of "diving for the cross" became part of a long and extended liturgy. This tradition occurs in the United States and Canada as well. Here's how it goes:
Essentially, as the bishop or archbishop finishes his prayers from a platform on the coast, a number of young men (perhaps 100) wait anxiously on small boats for the bishop to toss the coveted prize into the water - a large cross. At the point which the bishop makes the throw, every able young man makes the dive (the water being cold or warm), hoping to retrieve the valued possession. However, only "one" boy can be the victor, and to him is somehow bequeathed "good luck" for an entire year.
The practice persists today and is something quite foreign and superstitious to Christianity.