Fan made Left 4 Dead map lets you fight the battle of Helm's Deep
A Left 4 Dead mapper has painstakingly recreated the fortress of Helm's Deep from Lord of the Rings in the form of a huge Left 4 Dead survival map, which means you can create Gimli and Legolas' competition to slay the most enemies over the course of the battle, only this time using assault rifles instead of a bow and an axe. If you don't have the Zombie Genocidest achievement for killing 53,595 zombies yet, this map might be a good way to get it.
The three walls of Helm's Deep have been faithfully recreated, meaning you'll have to fall back deeper and deeper into the fortress as the zombies press, much like the defending forces were forced to in Lord of the Rings. The Left 4 Dead Survivors do get a few advantages over their Tolkien counterparts, though, like four mounted machine guns on the outer wall of the fortress. On the other hand: no Gandalf, so they're probably even. You can download the level from Left 4 Dead maps. Here's a video of the new map.