Audiowalks
Teri Rueb (GPS triggered) http://www.terirueb.net/i_index.html HP travel companion she used, files and explanation here: http://web.uni-weimar.de/medien/wiki/Teri_Rueb
Video walks
Janet Cardiff (also the Video-Walks!) http://www.cardiffmiller.com/artworks/walks/index.html call there and ask if it's still on (and let me know, then i also wanna go): http://www.jena1806.de documentary: http://www.youtube.com/watch?v=AKXXkxD3ue4
Karl Heinz Stenz und Winfried Wrede: http://www.theaterwrede.de/dedv.htm
commercial
a company specializing on audiowalks: http://www.soundwalk.com