Free City Help needed

I found this Free City in the assets store. http://forum.unity3d.com/threads/82974-Huge-City-Free I imported it, but didt know how to get it into my terrain. Someone, please help

Drag and drop it into the scene view, it wants to go above your terrain not into it

ok, thats what I thought too. But which of the files/folders/prefabs am I to drag and drop?