I'm searching everywhere for it, but I can't find it.




Ps: I'm at browser, NOT galaxy gog.

Welcome to the forums.

Assuming that you bought the game here, you don't get a serial key in a normal scenario. You will get a GIFT CODE if you buy the game as a gift for someone else, which they can redeem to get the game.
If you have just bought the game then you'll just have to go to your LIBRARY page [click on your user name on the top bar and click Games] and you will find your games there. You can download it from there easily using any of the three methods.

1. Use your Browser or its downloader plugins to download the game. Click on the game's thumbnail to see available downloads of both your game and bonus contents. In case on The Witcher 2 you have a 13 part download for the main game, download all the files in a single folder and run the setup to install it.
2. You can use GOGdownloader software to download a game. You'll need to download it. And then go to your library, click on the game thumbnail and instead of downloading gamefiles like previous option you need to click MORE and then GOG DOWNLOADER LINKS. A new page will open with links that will open with GOGdownloader and download the entireity of game files in one go.
3. You can use GOG Galaxy to download Offline installer similar to option one, or you can install the game the game by simply pressing Install. Both are Accessed from the Library tab.

See this link for the support page :
https://support.gog.com/hc/en-us/articles/212183569-What-download-options-are-available-
Hope this solves your problems. :)