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ART+COM have just launched a project called Timescope, which is allows you to visually travel through time using a telescope like the ones commonly mounted on the top of historic buildings.
Instead of zooming in and out over distance, you do it over time so that you can see how the cityscape has changed over the years. In Berlin it has obviously changed a great deal thanks to the World Wars.
More info and the Berlin site here.
(Images stolen from ART+COM).