We're getting close to the end here. :)
Herod learns that the Magi have ditched him and is 'unhappy'.
He sends out assassins and has them kill all of the children who were two and under. I actually came across a quote today from, drum roll please, Caesar Augustus. He heard that Herod had ordered all of the boys two and under killed, and his (Herod) own son was among that number. Caesar Augustus is reported to have said: "I would rather be Herod's pig than Herod's son."
Here's a link to OrthodoxWiki about the Massacre of the Holy Innocents.
Mary hears of Herod's slaughter and takes the infant Christ, swaddles Him and lays him in an ox-manger to hide Him.
At the same time, St. John the Forerunner is only six months old. Elizabeth takes him and runs into the hill-country. She tries to find a place to hide, but can't find anywhere. Tired and afraid, unable to climb any higher, she cries out: "O mountain of God, receive a mother and her child." Immediately the mountain splits open and receives them. The text says "And that mountain became translucent to them, and an angel of the Lord was with them and protected them."
The note says that the Greek used says 'diaphanous' for what happened to the mountain. So, according to the Online Etymology Dictionary, the Greek translates 'to show through'. So did the mountain become see through? Not a very good hiding place, unless it was like a one way mirror, where they could see out but no one could see in. Maybe it just means that they found a cave system and could watch people searching for them without being seen themselves.
The tradition holds that Elizabeth lived there with John for the rest of her life. When John was grown, he came out of the wilderness as a powerful preacher.