Alder

A long time ago, in a war to end all wars, the world was ruined, taking the vast majority of humanity with it. The people that remained worked together to create a city to stay in: Alder. The rich and powerful of them moved in and cut the city off from the rest of the world using a magical crystal. They also used this crystal to power Alder. Two-hundred years later, the crystal was stolen, and the city has been barely surviving ever since, slowly using the power that they had stored in case of an emergency. The city is currently run by The Council, a small group that holds an iron grip on Alder. Every five years, The Council sends a group of six orphan kids to go look for the crystal, but no one has found it.
There are no plants in Alder, everything from food to air is manufactured. There is no weather, it is always the same temperature and humidity, but there is a sun. There are a few small animals, but they are very rare. Everyone speaks the same language, with more or less the same accent due to no exposure to the outside world. There are a few villages outside of Alder, as well as plants and animals.