This wasn't on the EMS, but this seems to be the best board to post this on?
A father and son team claim to have decoded a piece of medieval music "built into" a medieval chapel in Midlothian:
http://news.bbc.co.uk/2/hi/uk_news/scotland/edinburgh_and_east/6605767.stmIf it's true, it would not be the only example of a direct relationship between medieval architecture and music (the famous motet for the dedication of Padua Cathedral being a well-known example), but I don't know of another where the music is actually written on the cathedral walls?