Leftover from Humble Deep Silver Bundle 2. It's a Humble Gift link (hope you've got an account already).

Enjoy your time in Stilwater, you'll be kicked out afterwards though...

It shouldn't be region-locked from what I've read.

Region-locked:
https://www.steamgifts.com/discussion/Rm5bO/humble-bundle-deep-silver-2-bundle-region-locked