Do you have FileVault enabled? Which mac OS X version do you use? Where is that file exactly?
http://en.wikipedia.org/wiki/Sparse_image, found via searching for "sparsebundle" or so.
sparsebundle is a timemachine image....
So TimeMachine is turned off?
Alright, so where is this folder located? Home folder?
Forgot to ask this before, but what name does it have and where in the home folder is it?
Oddly enough i went from 20 to 12 gigs when I just tested it today... what is this thing?!?!
A sparse bundle is an expanding disk image, normally they hold applicaitons that you download off of the Internet, or DVD images/etc.
It seems like you have created this, and then forgotten about it. Double click it to open it and see what is inside! If you don't need it, delete it.
Odds are, if FileVault is enabled, it's already open.
FileVault uses encrypted sparse disk images to encrypt your home folder. It then mounts them in place of your home folder when you log in. The location and size matches up.
http://osxdaily.com/2011/09/28/disable-time-machine-local-backups-in-mac-os-x-lion/
It's probably the local time machine backup, which is enabled by default in lion. See the link for how to disable it, if you want.