And it's just what you may be imagining - (except maybe you didn't expect it ALSO to be organ): there's a specific order in which you need to open and close certain drawers and such, to open a secret compartment. It took him years.
This is the artist:
https://en.wikipedia.org/wiki/Kagen_Sound
Details of the desk:
http://www.kagenschaefer.com/pipeorgandesk.html
In action:
Just thought I'd give you a heads up.