Portal 2 Levelpack

You need to have a copy of Portal 2 to play it. The level pack is available from the Steam Workshop. 

1. Click the download button to go to the Steam Workshop link and click "Subscribe from all" to get all of the levels.
    
2. Open Portal 2 and go to Community Test Chambers -> Play Single Player Chambers.
    
3. In the list there should be the three levels, 
   1. St. Eriksplan: Tutorial.
   2. Gosia: Intermediate.
   3. Poznan : Advanced.
       
4. Select one of them and click "Play" on the bottom left.
    
5. Enjoy!