Shoot ALL of the barrels in level 3 and a bridge will appear which you can then cross to get over the acid pit to reach the door. Enter the room and kill ALL the enemies and find the hidden exit and activate it to access the secret level.

On the 'Hurt Me Plenty' or higher difficulty setting get a 100% kill rating on any level.

On Nightmare difficulty setting beat any level to receive a Gamer icon of a Demon.

Complete the following achievements to get the corresponding GamerScore.

Clean Slate - GamerScore 5:
On 'Hurt Me Plenty' or higher kill ALL monsters in level.

Hoarder - GamerScore 5:
Find ALL items in level.

Scout - GamerScore 5:
Find a secret area of a map.

Rookie - GamerScore 10:
On Xbox Live get 50 kills.

Destroyer - GamerScore 10:
On Xbox Live get 100 kills.

Nightmare - GamerScore 10:
In Single Player mode win a Nightmare level.

Neophyte - GamerScore 20:
Complete any level.

Episode 1 - GamerScore 25:
On 'Hurt Me Plenty' or higherComplete Episode 1.

Episode 2 - GamerScore 25:
On 'Hurt Me Plenty' or higher complete Episode 2.

Episode 3 - GamerScore 25:
On 'Hurt Me Plenty' or higher complete Episode 3.

Episode 4 - GamerScore 25:
On 'Hurt Me Plenty' or higher complete Episode 4.

Rampage - GamerScore 35:
On UltraViolent mode complete ALL levels.