Making AI that can navigate through a city?

I’m making a game where people live in a city and each person is going somewhere or doing something. I need a way for these people to find a route to a destination that is entirely unobstructed. I need these people to be reasonably smart and understand that if an object is in front of them, they need to find another route. Any ideas of how I can accomplish this? Thanks in advance!

use pro, use the navmesh.

If you dont have pro activate the 30 day eval.

Try the manual: http://docs.unity3d.com/Documentation/Manual/NavmeshandPathfinding.html

I figured out that I can use the A* algorithm. All is well. Thanks!