There have been several times when I’ve seen a Safari download sitting on my desktop unfinished. I’ve wondered where it came from (the URL) and what exactly was contained inside. Unfortunately for me, these things always seemed to remain a mystery as I dragged the download into the trash. The Mac DevCenter, however, has a solution to the mystery with a control-click and “Show Package Contents”:
Inside you'll find the download itself and an Info.plist file. To view the property list file, just drag it onto TextEdit to open. Properties include the URL source of the file, the date and time of the download, and the progress to date.
Good to know. Files that end in “.download” are no longer a mystery.