The project was initiated by the net label Autres Directions In Music. The brief was for 30 musicians from 30 different cities to sample environmental sounds and then to rework them into musical pieces without adding beats and other sounds. They also had to accompany their tune with text about their piece and a image "of a space in their city that they like for its acoustic value." In doing so Autres Directions In Music hoped to create a "journey through music, we imagined a route through the world" which would eventually take us through San Fransisco, Lima, Barcelona, Paris, Moscow, Melbourne, Manchester and St Petersburg as well as many places between. Not only have the tunes been give to of for free, via the Creative Commons Licence, but the team have also created and distributed all the artwork for the release. The download page can be found here and there's a handy folder link so that you can get the whole thing in one (hefty) download.
The Noise & The City - I'm sitting at home listening to The Noise & The City and it's really great (think Autechre, The Future Sound Of London & the mellower, more musical side of Aphex Twin and you'll be heading in the right direction).