Sacrum

Sacrum is the first official level in Prodeus and serves as an introduction to the first few weapons and enemies of the game. It is the level where the player first gets the Shotgun and the Shredders, and the first level where Zombies, Fiends, Shotgun Zombies, and Bloaters are fought. Chaos ammo can be found throughout the level, usually in secrets, but there are no chaos weapons available at this point making them only useful for repeat collection. It is followed by Research.

Secrets

 * 1) After collecting the Shotgun and killing some Zombies, the player can interact with an unmarked door to access an outdoor area. From here, climb the rocks until you find a panel and step on. Reward: Large Chaos Ammo
 * 2) At the red key elevator, climb on top and jump over the nearby glass wall. Reward: Large Armor
 * 3) Immediately after secret 2, head outside and jump on the rocks next to the stairs. Reward: Small Chaos Ammo
 * 4) Shortly after collecting the Shredders, activate a fake wall. Reward: Large Chaos Ammo
 * 5) After collecting the red key, explore the rock wall to discover a staircase back to the previous areas.

Secret Exit : Shortly after fighting your first Fiend, a hidden ledge can be jumped to containing the first secret exit of the game. This exit does not lead you to Ammo Cache like the others, rather it leads you to a portal connecting the start of the area with the Citadel. While this could allow for early access to this level, the level is locked behind a rune requirement.