In the words of the Cities and Memory site:

What is Cities & Memory?

Cities and Memory is a global field recording & sound art work that presents both the present reality of a place, but also its imagined, alternative counterpart – remixing the world, one sound at time. Every faithful field recording document on the sound map is accompanied by a reworking, a processing or an interpretation that imagines that place and time as somewhere else, somewhere new. The listener can choose to explore locations through their actual sounds, to explore reimagined interpretations of what those places could be – or to flip between the two different sound worlds at leisure.