Options/ advanced/ console. Its on the right handside. Then press~. If you put maplist press Enter You get the map list. Double click on 4l0 and you get the level that wasn't in the game.
what the hell, I'll just repost the same thing as everyone else to get more posts because I'm a loser...
when you first start up the game, go to options, advanced (at the top) then make sure 'Console' is checked. Then in the game press the ~ key and it console will appear instead of the chat window.