Well-known applications like Google Earth and Virtual Earth not only give you the possibility to hover above earth but to discover some cities by switching on a three-dimensional view thus giving you a hint of the city's appearance. I sometimes wish that it would be possible to visit historical sites as well. The Rome Reborn Project makes this possible with a 3D model of the eternal city. Now there's a new approach by Frank Dellaert at the Georgia Institute of Technology in Atlanta, together with his colleague Grant Schindler and Sing Bing Kang of Microsoft's research lab in Redmond, Washington. Their software constructs an animated 3D model that shows the change of a city over the years.
Coming from old photographs of the site, the 4D cities software automatically arranges these photographs according to their common features until the visibility patterns of all the buildings are consistent. It then computes a 3D animation of the city, allowing a visitor to travel through time. (Source)