The Summer Mapping Initiative was a contest where community developers could show their stuff to the Portal 2 team. Valve noted that there were 280 entries into the creation contest which were whittled down to just a handful of the best designed content to proclaim a victor. All of the maps that were entered into the contest are free to download from Thinking With Portals then uploading them into your Portal 2 maps file via your Steam folder on your PC.
Here’s a more detailed explanation of the process:
1) Download the map file from ThinkingWithPortals.com.
2) Open up the .ZIP file after it has downloaded.
3) Find the location of your Portal 2 installation on Steam. This is most typically found under:
Windows PC users: C:Program FilesValveSteamsteamappscommonportal 2maps.
Mac users: ~/Library/Application Support/Steam/SteamApps/common/Portal 2/portal2/maps
Note that your installation location may vary, depending on your initial install directory.
4) Copy the .BSP file located in the downloaded file to the directory above.
5) Start Portal 2
6) In the game’s main menu, select “Options->Keyboard and Mouse”
7) Set Allow Developer Console to Enabled
8) Press the tilde (~) key to access the console
9) Type map “mapname here”
10) Solve the puzzle!
It’s a win/win these community developers get some cool swag and the glory of being pronounced the top dogs by Valve themselves, and we get new maps.