Our character is not very smart-it can collide with objects, but it cannot do any path finding. You can implement a 3D path finding solution (based on a graph of points in space, for instance) or use one from the Asset Store. You can also use Unity's standard built-in NavMesh Agent to find the path on the terrain and only control the height of the character.

You can also switch between flying and walking modes by setting a target point on the ground for the character to land, checking the ground with a Physics.Raycast() method, and turning the gravity back on and implementing the Using root motion to steer a character recipe to move the character when grounded.