Crossing the First Threshold

Now comes the really juicy part of the story. After meeting with the Mentor, the Hero crosses the first threshold into the Special World. Gone are the doubts and excuses, gone are the fears and protestations. The Hero commits to the journey, for better or worse. Usually something happens to spur this kind of commitment in the Hero, such as the raising of stakes or intensifying of motivation.
Often at the Threshold lives the Threshold Guardian (big surprise there), who must be overcome in order to cross the Threshold. After doing so, the Hero crosses in to the Special World and commences Act II of his Journey.
Sometimes the Special World is not as glittering as the Hero thought. Sometimes the other side of the Threshold is dark, disorienting, dismal. Commitment is not the only problem the Hero faces. After committing there are tests, enemies, and challenges throughout the Journey. Sometimes a problem comes up immediately after the Threshold has been crossed.
The Second Act is when the Hero can put to use the advice, experience, and equipment the Mentor has supplied him with. The Mentor may accompany the Hero on his Journey (think Gandalf and Frodo), but more often he stays behind in the Ordinary World and lets the Hero exercise his new abilities.
The Threshold is often a physical barrier or portal that must be crossed. It could be a bridge, gate, river, international border, tunnel, mountain pass, or anything else that symbolizes the border between Ordinary and Special Worlds.
Crossing the first Threshold is not the end of the Hero's difficulties. It may be just the beginning, in fact.