If you pre-ordered Borderlands 2, then you should have entered a code to access the Creature Slaughter Dome, but how the hell do you find it?
Well, it’s a little ways into the game, so you won’t have access to it immediately.
Once you get to the Wildlife Exploitation Reserve, then you’ll be able to enter the arena, but don’t go looking for Creature Slaughter Dome, because it’s actually called something else in the game.
On the east side of the map in the Wildlife Exploitation Reserve, look for a building with HYPERION written above the entrance. Go inside and look to your right and you’ll see an easy to miss door, which takes you to the Natural Selection Annex, which is the in game name for the Creature Slaughter Dome.