Name: Quake II (GOG)
Brand: id Software
SKU: KT-11C1837C02
Price: 7.54 EUR
Availability: InStock

Shortly after landing on an alien surface, you learn that hundreds of your men have been reduced to just a few. Now you must fight your way through heavily fortified military installations, lower the city's defenses and shut down the enemy's war machine. Only then will the fate of humanity be known.

Redeem on GOG

You need a GOG account.

Step 1: Go to gog.com/redeem and sign in.
Step 2: Enter the key.
Step 3: Confirm. The game appears in your GOG library.

GOG's redeem page Full guide for GOG

Activation notes from the publisher

Go to: http://store.steampowered.com/ and download STEAM client Click "Install Steam" (from the upper right corner) Install and start application, login with your Account name and Password (create one if you don't have). Please follow these instructions to activate a new retail purchase on Steam: Launch Steam and log into your Steam account. Click the Games Menu. Choose Activate a Product on Steam... Follow the onscreen instructions to complete the process. After successful code verification go to the "MY GAMES" tab and start downloading.