I just found this today. It is so inspiring - I wish I could have been there. I hope you enjoy it as well!
This occurred at the Wannamaker Building in Philadelphia, which houses the largest pipe organ in the world... now there is a Macy's in the building. Six hundred choristers from the Philadelphia Opera Chorus spontaneously broke into the Hallelujah Chorus. I love to watch the looks on the faces of the observers!
For more information about the event, click here.
