Take a small cardboard robot that moves in one direction only, afix an indication of its final destination and let people make sure it gets there.
This is the concept behind TweenBots. This is a really cute example of the "wisdom of crowds" concept. Basically the same principals that make things like Wikipedia or the Mechanical Turk Dollar Bill (also known as Ten Thousand Cents ) possible.
In this case instead of the robot developer building in expensive navigation equipment, she uses a simple flag to indicate the robots final destination and let people help it out along the way. It is probably not the most efficient path, but if you consider the time invested in total by the developer and all the 29 people who intervened to navigate the robot through the park and compare that to the effort it would take to incorporate navigation... well you begin to see how competitive a proposition like this becomes.
The result is a very cute video, and a super cool concept.