More than 35,000 maps have been created by fans in the two days since the launch of the game's 'Perpetual Testing Initiative' update, reports Eurogamer.
The update includes an easy-to-use editing tool that allows users to create their own puzzle rooms and share them to the Steam Workshop for other users to download.
The Steam Workshop launched in February along with mod creation tools for The Elder Scrolls V: Skyrim. Valve released its own Portal-themed Skyrim mod featuring the Space Core.
To celebrate the launch of the new Portal 2 update, Valve has slashed the game's price on Steam to £5.09 /$6.79 until May 11.
There are no plans for the 'Perpetual Testing Initiative' DLC to be released on Xbox 360 or PlayStation 3.
Valve released Portal 2 for Xbox 360, PC and PlayStation 3 in April 2011.