a cliff, and looking over the edge, they see a shocking sight.

They looked out into a cave so enormous that it seemed almost as big as the world outside. Far down at the bottom shone a cluster of lights.

"It’s Ember," Lina whispered ...."Oh, our city, Doon. Our city is at the bottom of a hole!" She gazed down through the gulf, and all of what she had believed about the world began to slowly break apart.

As incomprehensible as it is to Doon and Lina, in seeing their city from above, they realize that they have lived their entire lives not just in a separate world, but underground. They realize that there is a surface to the world with a sky above it, that this is where they have escaped to, and that Ember and all its citizens have lived for hundreds of years below the surface of the Earth. They also realize that this is where their ancestors always meant for them to come back to. It is time for the people of Ember to return to the surface world. It is with this knowledge that they send their message down to Ember and beckon their people back into the light.

In Jeanne DuPrau's sci-fi novel The City of Ember, twelve-year-old characters Lina and Doon are citizens of a post-apocalyptic society, living in an underground city called Ember. Together, the two work to figure out important instructions left behind by the city's founders, as well as why Ember's electrical system is failing and food supplies are disappearing.

In chapter 12, which is titled "A Dreadful Discovery," Doon returns to the locked door in tunnel 351 only to discover there is now a key sitting in the lock. When he opens up the door, he finds a "brightly lit room" that is filled to the brim with "mounds of cans, heaps of clothes, rows of jars and bottles, stacks of light-bulb packages." These are all valuable, necessary resources that are being kept from the people of Ember. Doon also sees "a great blob of a person" asleep in a chair, with a plate smeared with food in front of him. While talking with Lina later on that day, Doon tells her that the person he saw is the mayor of Ember, who has apparently been stealing and hoarding these supplies for himself with help from Looper.

Doon and Lina have spent their entire lives underground, so when they exit the tunnel and emerge into the aboveground world, there are many things that they encounter that are completely alien to them, mostly related to the natural world, which they have been cut off from. The first new thing they see is the sky. They see the night sky with the moon and stars, and at first, they believe the stars are the lights of some distant city like Ember. It isn't until the sun rises that they understand that the sky is a changeable thing, unlike the cave ceiling in Ember.

The sunrise is another new and shocking thing that Doon and Lina see. DuPrau shows how unfamiliar the vision of a sunrise is to them by describing it in very imagery-laden and specific language, as if Doon and Lina are trying to capture each moment of this new experience:

The edge of the sky turned gray, and then pale orange, and then deep fiery crimson. The land stood out against it, a long black rolling line. One spot along this line grew so bright they could hardly look at it, so bright it seemed to take a bite out of the land. It rose higher and higher until they could see that it was a fiery circle, first deep orange and then yellow, and too bright to look at any longer. The color seeped out of the sky and washed over the land.

They also experience flora and fauna for the first time. They feel grass beneath their feet and eat fruit from a plum tree. They see birds flying through the air and even encounter a fox as they walk, but thankfully, they do not upset it.