See games such as Homeworld or Sins of the Solar Empire. These take place in 3D environments (outer space) with no “hard walls”: rather than explicitly forbidding you from leaving the “game zone”, there simply is no point to. There’s so much empty space between galaxies that you would never be able to fly from one galaxy to another before getting terribly bored with the game. So players are strongly motivated to stay within the star systems where the real action is.
Also, in the same way you can construct a finite but boundary-less 2D universe for your game (e.g. a universe on the surface of a sphere, or a universe on the surface of a torus), you can also construct a finite but boundary-less 3D universe for your game.
See games such as Homeworld or Sins of the Solar Empire. These take place in 3D environments (outer space) with no “hard walls”: rather than explicitly forbidding you from leaving the “game zone”, there simply is no point to. There’s so much empty space between galaxies that you would never be able to fly from one galaxy to another before getting terribly bored with the game. So players are strongly motivated to stay within the star systems where the real action is.
Also, in the same way you can construct a finite but boundary-less 2D universe for your game (e.g. a universe on the surface of a sphere, or a universe on the surface of a torus), you can also construct a finite but boundary-less 3D universe for your game.