I was visiting Rosslyn Chapel a while ago and tried the acoustics of the crypt. The music that immediately came to mind was the mediaeval chant "Vexilla Regis". I sang a couple of verses - meanwhile upstairs, some other visitors asked my girlfriend what the choir was.

When I can borrow a good digital recorder from somewhere, I'll go back and do some guerrilla recording on ocarina or alto flute.

The best echo in Britain is at the mausoleum of the Dukes of Hamilton, near Hamilton in western Scotland. Longer and stronger than St Pauls Cathedral. The building is a hollow tower like a great big salt shaker. The echo is so powerful you can't think of playing tunes, instead you do very slow-moving chord progressions built up out of your own echoes. It's full of Masonic symbolism, which I guess opens another can of worms. I've quite often been at music events in Masonic halls.