Doom The Dark Ages is one of the most popular total conversion mods for the original Doom, and Chapter 20, titled ‘Fallen Citadel’, is widely considered the hardest level in the entire campaign. It’s packed with tight corridors, surprise demon spawns, and so many hidden walls that even seasoned retro FPS players can get lost for hours trying to find all the content. If you’ve spent the last hour running in circles through the foggy, demon-infested ruins of Chapter 20, you’re not alone. Most players miss half the hidden content on their first playthrough, and many never even find the secret exit that skips three of the hardest combat waves. We’ve put together this deep dive into doom the dark ages chapter 20 secrets after running 12 full playthroughs, testing every wall crack, item pickup, and enemy spawn to pull out every hidden trick you can use. You won’t find generic basic walkthrough steps here – we’re focusing only on the stuff 90% of players miss on their first 3 runs.
Doom The Dark Ages Chapter 20 Secrets: Hidden Collectibles You’re Probably Missing
Most of these doom the dark ages chapter 20 secrets are intentionally hidden to reward players who take their time exploring, instead of rushing through the level to beat it as fast as possible. The three hidden runes scattered across the level are the most important collectibles, as they unlock unique perks you can’t get anywhere else in the campaign. You’ll find the first rune behind a fake wall in the opening courtyard, the second tucked under the raised drawbridge, and the third behind a movable sacrificial bowl in the demon altar room. Each rune has a permanent or long-lasting perk that makes the rest of the chapter far easier:
- Blood Rune: Unlocks 20% extra damage for all demonic weapons for the rest of the chapter, no ammo cost for the first 10 shotgun shots after picking it up
- Shadow Rune: Makes you invisible to low-tier imps and zombies for 5 minutes, perfect for sneaking past the horde in the underground tunnel section
- Soul Rune: Grants an extra permanent life point that stays with you even after you beat the chapter, works for all subsequent playthroughs on the same save file
We’ve seen a lot of players write off these runes as useless cosmetic collectibles, but they make a massive difference even if you’re only playing the chapter once. The permanent extra life from the Soul Rune, for example, can save you from a game over in the final boss fight of the entire campaign later on, so it’s well worth going out of your way to grab it. If you’re playing on hard difficulty, the 20% extra damage from the Blood Rune will cut the regular end boss’s fight time in half, so you don’t have to burn through all your ammo just to take him down. You can also combine the Shadow Rune with the invisibility powerup you find in the sewer to be completely undetectable for almost 10 minutes straight, letting you run through the entire level without fighting a single regular enemy if you want.
Secret Shortcuts That Skip 30% of the Chapter’s Combat
You don’t have to fight every single demon spawn to beat Chapter 20, and most of the hardest waves are entirely skippable if you know where to look. This is one of the most useful doom the dark ages chapter 20 secrets for speedrunners, who use it to cut their total chapter time by almost 40%. The first shortcut is right after you pick up the rocket launcher in the armory. Most players walk out the main door and face the 15-demon horde in the courtyard, which includes two Hell Knights and a swarm of imps that can take out half your health before you even get a shot off. But if you shoot the vent grate above the weapon rack, you can climb up and crawl through to the other side of the courtyard, landing right next to the next story lever.
This shortcut does mean you miss the regular ammo pickup in the courtyard, so make sure you’ve got at least 10 shotgun shells and 5 rockets before you take it. Another secret shortcut is in the flooded sewer section. Most players spend 10 to 15 minutes navigating the maze of tunnels, fighting off underwater demons and getting lost trying to find the exit. But if you dive down to the very bottom of the leftmost tunnel right after you enter the sewer, you’ll find a hidden passage that leads directly to the boss antechamber, skipping the entire sewer maze entirely. You will need the underwater breathing powerup from the guard tower barracks to use this shortcut, otherwise you’ll run out of air halfway through the 20-second swim and die before you reach the other side. If you don’t have the powerup, you can still grab it by backtracking to the guard tower before you enter the sewer, it only takes 2 minutes to run back and get it.
How to Trigger the Secret Boss Fight for Exclusive Loot
90% of players only fight the standard Hell Knight boss at the end of Chapter 20, which drops a regular plasma rifle that you can find in almost any other level in the mod. But there’s a secret Archvile boss you can trigger that drops the unique Dark Spear weapon, which one-shots most regular enemies for the rest of the game. To trigger it, you need to collect all three of the runes we mentioned earlier, then place them in the three empty slots on the altar in the back of the boss room before you walk through the main red door that triggers the regular boss fight.
Wait, don’t place the runes until you’ve stocked up on ammo and health, because the second you place the third rune, the room locks and the Archvile spawns immediately, along with 8 supporting imps that spawn in the corners of the room. This boss is 2x as tough as the regular end boss, he can summon extra demons mid-fight and heal himself if you don’t keep constant pressure on him, so don’t try to trigger it on your first playthrough if you’re already low on resources. We recommend saving at least 20 rocket rounds and a full stack of shotgun shells before you trigger the fight, and make sure you have at least 2 extra health kits in your inventory. The Dark Spear you get for beating it is well worth the extra effort – it uses soul energy instead of regular ammo, so you never have to worry about reloading or running out of shots as long as you keep picking up enemy souls, and it can even one-shot the final campaign boss if you hit him in the weak point on his head.
Common Mistakes That Make You Miss Chapter 20’s Best Secrets
Even if you know where the secrets are, there are a few common mistakes that can lock you out of them permanently during a playthrough, forcing you to restart the entire level if you want to collect everything. The first one is lowering the drawbridge before you grab the Shadow Rune under it. Most players see the lever for the drawbridge right next to the guard tower exit and pull it immediately to get to the next section, but once the bridge is down, the rune gets crushed under the heavy wood, and you can’t get it anymore for that run. If you want the Shadow Rune, you have to jump down into the moat first, grab the rune, then climb back up to pull the lever.
Another mistake is killing the first wandering zombie priest in the courtyard before he walks over to the cracked wall. A lot of players shoot every enemy on sight as soon as they spawn, but if you let him walk to the wall first, he’ll hit it with his staff and expose the secret room with the Blood Rune, so you don’t have to waste ammo shooting every cracked wall in the courtyard to find it. He won’t attack you until he gets to the wall, so you can just hang back and wait for him to do the work for you. A lot of players also rush through the armory section without checking the vent for the shortcut, and end up wasting 10 minutes fighting the courtyard horde for no reason, even if they have enough ammo to take them out. Always take 10 seconds to check every cracked wall and unlabeled lever before you move on to the next area – that small habit will help you catch almost every hidden secret in the chapter without extra effort, and it’s a good trick to use for every level in the mod, not just Chapter 20.
You don’t have to spend 10 hours replaying the chapter over and over to find all its hidden content, or watch 20 different short walkthrough clips to piece together the best tricks. These doom the dark ages chapter 20 secrets will help you unlock every collectible, skip the most frustrating combat sections, and get the best exclusive loot in the level on your next playthrough, even if you’re playing on the hardest difficulty setting. If you try any of these tricks on your next run, make sure to note if you find any extra secrets we missed – the community is still uncovering new hidden bits of the level every month, even years after the mod first launched, and there are probably a few tiny Easter eggs no one has found yet.
