Do you have a 'Get Info' window open in the Finder?
Click on the Previewed image, or actually, double-click it, and you'll open/run the item displayed. This also opens a folder.
[crarko adds: This has been around a long time, but some folks may not know the tip.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20111217161044299