Recently I have downloaded the Witcher 2 Assassin of Kings, through the GOG downloader. I am curious as to where the files go, so that I can start the game up. I am sorry if this sounds (or is) a stupid question.

Thanks

Right-click the game in the downloader, then select "Open enclosing folder".

When you click the "Settings" button, there's a field "Save downloads to:", which allows setting the target path. (I don't remember the default one, it might depend on the OS.)

The thing is, when I open the downloader, since I already downloaded the game, it doesn't show up.

It says that it was downloaded to My Documents/GOG Downloads, yet all I find there is a .bin file, which decides to play in the SMP video player

*.bin files (assuming they're downloaded from GOG) are actually part of large installers: they're not video files, but data containers. There should normally be an *.exe file in the same location, which unpacks them during the installation...

Hmm.. No .exe file to be seen there

Witcher 2 installer is very, very multi-part. Plus, the downloader normally creates a subfolder for each game, named accordingly.