Lots of Finder windows opening all at once

Last Sunday I was looking through Finder on my mid-2011 MBA. (I was clearing out my 'cache' and 'preferences' folders.) I must have either clicked something (I use an external mouse) or pressed something on my keyboard because suddenly all the folders started opening in separate Finder windows! There were lots of them and they completely covered the screen! But then I closed all the folders (when they'd finished opening...) and my screen looked normal again. Is there a menu option for 'opening finder folders in individual windows' or something?? Or a key combination that I was unaware of? Grateful for any help - intrigued!

Thanks

Harry