I don't know why but I have almost 200 virtual desktops and I'm looking for a way to just have one open.
Usually I hit F3 go to one and kill it. But to do it 200 times it's gonna take a lot of time!
Only some references, give some attempts.
Ask Different site: Close empty desktop/spaces  [Aug 10 '14]
You can speed this up and hold Option down and this will keep the (x) to close the desktops shown so you don't have to hover over the selected desktop and wait for it to show itself.
The only way that I would think you might be able close them all at once without performing the above process is probably with an automator script or apple script.
"Close Desktop Spaces in Mission Control for Mac OS X Quickly" 
There are other ways to close the virtual spaces but, remember, you can quickly close desktop spaces in Mac OS X Mission Control by holding down the Option key, this causes the familiar iOS style and Launchpad (X) close symbol to appear over the spaces which can then be rapidly closed.
"Handy Keyboard Shortcuts for OS X Mavericks" 
Close All Windows
sometimes, the kevinslist's way cannot work as your wish, try these:
NOTE that the preferences of your Dock Bar will be reset too. It's foolish but only a way to force the world clean.