In Anthem, what lies beyond the city, and why has Equality 7-2521 never been there?
Beyond the city is the Uncharted Forest. The first thing we hear about the forest from Equality 7-2521 is that this area is so restricted that the leaders have made a rule forbidding thoughts about it.
Beyond the ravine there is a plain, and beyond the plain there lies the Uncharted Forest, about which men must not think.
He goes on to explain that men do not go into the forest because there are no trails, and because wild animals kill and eat whoever enters before long. Later, Equality 7-2521 finds out that it is actually quite possible to traverse the Uncharted Forest. He is able to keep the animals away by building a fire every night, and feeds himself by hunting and killing his own food.
The Uncharted Forest symbolizes previously forbidden possibilities and independence. At first glance, the Uncharted Forest is simply a place that is forbidden to enter. However, it goes deeper than that. Not only was entry forbidden, the leaders went so far as to convince the people that they would not be able to survive in the forest on their own.
Men never enter the Uncharted Forest, for there is no power to explore it and no path to lead among its ancient trees which stand as guards of ancient secrets.... These men do not return. They perish from hunger and from the claws of the wild beasts which roam the forest.
When he is forced to run to the Uncharted Forest to protect the box, Equality 7-2521 finds out that he is perfectly capable of keeping himself alive, proving to himself that he can survive independently of the collective.
After Liberty 5-3000 (The Golden One) joins him, Equality 7-2521 and Liberty 5-3000 travel through the Uncharted Forest and find mountain ranges beyond the forest. They find an old house, a relic from the Unmentionable Times, and settle there.