The Art of Navigation
Navigation is the process of purposefully steering the course of an entity through a physical medium. Navigation is autonomous when a "system" can steer its own course unassisted (like most mammals). Navigation is one of the possible causes of movement. As a proactive behavior, navigation differs from plain movement, which is more of a passive consequence of the physical rules in the world (for instance, an object falling off a cliff).
To navigate, a human or animal must perform actions that produce movement. In biological creatures, the actions are executed by using combinations of muscles. This can result in walking, running, or crawling depending on the circumstances. The AI will generally not need the same precision in control as mammals, so we'll probably need simpler actions to emulate the important behaviors in nonplayer characters (NPCs).
Purposeful navigation in a cluttered world is not possible just by executing actions. Try walking through an unknown door without looking or feeling walls. In this case, reaching the other side is probably more a question of luck than intelligence. Information about the surroundings needs to be gathered beforehand.
For biological creatures, much of the complexity of navigation arises from the acquisition of information. This may be done in a variety of ways, including the use of physical sensors (for example, feeling contact with the floor, collision with walls) or visual sensors (for instance, seeing a doorway, ledge, or obstacle). A rough description of space is encoded in these perceptions; both the empty areas as well as the solid ones can be picked out. Humans and animals must understand these before they can consider intelligent movement.
Evolution has allowed biological creatures to become particularly efficient at what they do. As AI engineers, it's much tougher for us to re-create this without billion years of survival of the fittest.