Because we are aiming for state-of-the-art NPC intelligence, nothing less than complex 3D worlds will be satisfactory—like those humans deal with. This needs to be an environment frequently used by human players, and not a simplified test bed for the sake of AI development. By keeping the experimentation process up to standard with the realism of actual game worlds, fewer problems will arise due to fundamentally flawed assumptions. Keeping the test "levels" and scenarios diverse will unconsciously prevent these problems. Such guidelines need to be followed throughout the development of the movement.
To be realistic, it should include doors and corridors, stairs and ladders, narrow ledges and dead ends, floors with gaps and irregular terrain, closed rooms and open spaces, jump pads and teleporters.
Now that the environments have been explained and defined, our focus can be set on the actual movement. As discussed, the world has a very important impact on the movement, but it takes certain capabilities from games characters to use it to their advantage.