Crossing the First Threshold
And Jesus, full of the Holy Spirit, returned from the Jordan and was led by the Spirit in the wilderness for forty days, being tempted by the devil.
Luke 4:1-2
After meeting with the Mentor and finally accepting the Call to Adventure, the Hero must leave the Ordinary World and enter the Special World. Doing so means crossing a clear line from one world to the next. The Fellowship of the Ring shows it beautifully. When Frodo and Sam are leaving the Shire, the countryside actually changes color as Sam pauses and says, "If I take one more step, it'll be the farthest away from home I've ever been." In screenwriting terms, this marks the end of act one.
Crossing the First Threshold can take a moment, just a beat of acknowledgment, or several minutes, depending of the needs of the story. Sometimes we'll see another archetype: the Threshold Guardian. In the nearly forgotten fantasy film Stardust, the threshold is a literal wall, and the Threshold Guardian is a literal guard. Getting past him and into the Special World requires effort and cunning. Nothing worthwhile ever comes easily, and our heroes must earn every step. Even Sam's reluctance to leave the Shire acts as its own sort of the Threshold Guardian.