Google Maps has added walking directions. It's a great idea, but it definitely deserves their "beta" designation.
To test it, I asked it for directions from somewhere vaguely near my house to Shelby Park, and it came up with six possible locations for the latter. You can see the result for the location I chose here. Google Maps and Mapquest are both very sketchy about the park. For example, Google shows the nature center in the wrong place. You can drag endpoints, but if I was actually looking for directions, presumably I wouldn't know the location was wrong. Moreover, you can only drag it to what Google recognizes as a street, not to where the center actually is. The map doesn't show all the park roads, including a major entrance off where Lillian dead-ends into the park and the parking lot for the nature center.
The biggest drawback is that Google Maps still relies on roads only. It's smart enough to know you can walk on one-way streets, but it doesn't know anything about non-motorized paths. There is a trail from the dog park (not shown, but it's where Lillian dead-ends) that runs into the park. The greenway isn't shown, nor is the new pedestrian bridge across the river to the Stones River greenway. The upshot is that the path it show me is more direct than it driving path it shows, but it's still not the fastest way to get there.