When you begin a game of Dwarf Fortress, you create an enduring world that will remain for the duration of your game. Everything in this world, of course, is continuously changing. Civilizations grow, go to war, and get destroyed, and you can always try to intervene as and when you see fit.
The depth of the gameplay is amazing, it goes from fighting enemies alone in the depths of a dungeon, to recruiting fellow travelers and building gadgets, while accepting missions and gaining reputation in whatever region you find ourselves.
As a small example to give you an idea of the sheer magnitude of Dwarf Fortress, there are over two hundred different types of rock in the game, all geologically placed where you would logically expect them in the real world.
Dwarf Fortress is an enormous and demanding game. The learning curve is devastating, and getting to grips with the controls and adjusting yourself to its rough visuals, can take quite a while. However, the players who do persevere will find a truly unique experience.