The fanmade map Helm's Deep – wherein Left 4 Dead 2 players attempt to defend the iconic Lord of the Rings castle fortress from relentless hordes of the undead – is now an officially supported map.
It's part of the latest update to Left 4 Dead 2, which addresses consistency issues when playing on dedicated servers – Valve also decided to add Helm's Deep to the official servers list. If you want to add the map to your game, all you have to do is head to the Steam Workshop page for Helm's Deep Reborn and click to subscribe to download the map.
The Steam beta version of Left 4 Dead 2 recently added an Extended Mutation system, where players could tweak existing game types and maps or come up with entirely new ones of their own design. To date, the Left 4 Dead series hassold more than 12 million copies.