What is the threshold Amundsen has to pass in order to continue on his journey?

To continue his journey, Amundsen must pass the threshold of the Antarctic Circle, which is located at approximately 66.5 degrees south latitude. This geographical boundary marks the point where he can access the polar regions, allowing him to proceed with his exploration of Antarctica. Crossing this threshold is significant as it symbolizes the transition into the harsh and challenging environment of the polar frontier.