This is the work of James Rojas and his team. It's a model of an imagined downtown L.A. that would improve on the current downtown in a number of ways —on first glance, more colorful buildings, no cars, cute plastic animals in an enormous and hilly central park. If you want to know a little more about it, look here. This photo doesn't do the model justice, as it was something to behold.
On the subject of an improved downtown and Park(ing) Day in general and what it's about, it's worth noting that I missed a few sites downtown because traffic and parking both are less than easy in that vicinity.
I drove around on Park(ing) Day, and I looked for parking. Isn't that the problem? Next year, I'm taking the Xtracycle and getting around without a car.