Yesterday I did a post regarding various D&D modules that are considered to be "the best", and I included The Haunted Halls of Eveningstar as an example of a module that I feel should be in the top 10.
What I didn't mention is that I have run THHoE three separate times, once in AD&D 1st Edition, and twice in 5th Edition.
But the module is obviously AD&D... So how do you convert an old module to 5E???
Well, I shall tell you. And it is surprisingly easy.
Especially since adventures in older editions are significantly harder than modern editions and the PCs were weaker and more squishy back then, and PCs in modern editions are considerably over-powered in comparison. As a result it is pretty easy to convert modules and the only complaint to the DM should be "This is too easy!", but in order to challenge players I recommend that raise the hardness in some circumstances.
Also, in some cases when it comes to treasure I recommend nerfing some of the loot. Older modules sometimes gave out "Swords of Wishes" and similar overpowered objects.
But let's pretend that you are new to the whole idea of converting modules, so here's some DMing tips when doing so:
1. Start With Story, Not Stats
The soul of any adventure lies in its story, not the math behind the monsters. Before you open your Monster Manual, read the old module like a novel.
Ask yourself:
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What’s the adventure really about?
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What are the main themes or moral choices?
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Who are the key villains and what drives them?
By understanding the story first, you’ll avoid getting lost in the technical weeds. A well-told tale transcends edition mechanics.
2. Identify the Core Encounters
Every module has a few “signature” moments — the boss fight, the puzzle, the trap that everyone remembers. Circle or highlight these.
When converting, make sure these iconic encounters survive translation. You can tweak numbers or monsters later, but those tentpole moments are what give the module its flavor.
Example: In Ravenloft (I6), Strahd’s tragic duel in his castle is essential. Even if you change the spell list or stats, the scene must stay.
3. Match Challenge Ratings to Modern Balance
Classic modules were often deadlier (and less forgiving) than 5e adventures.
To avoid total-party-wipe frustration:
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Use Challenge Ratings (CRs) to approximate new monster stats.
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Adjust hit points or numbers rather than replacing every creature.
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Remember that 5e characters are generally tougher — healing, cantrips, and short rests change pacing dramatically.
A good rule of thumb:
For every 2E/Basic “hard encounter,” make it a “moderate” one in 5e. Players will still sweat, but it’ll feel fair.
4. Replace Obsolete Mechanics Gracefully
Old modules love saving throws vs. poison, THAC0, and weird initiative systems.
Instead of translating each one literally, interpret their intent.
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THAC0 → Attack bonus: Use the 5e equivalent for similar challenge levels.
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Save vs. Death/Poison → CON save: 5e’s Constitution saving throw covers most of these.
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Morale checks → Roleplay moments: Use NPC personality traits or Wisdom saves.
It’s better to reinterpret than to replicate. You’re adapting the spirit, not running a museum exhibit.
5. Rebalance Treasure and Magic
Classic loot tables can break modern games.
In early D&D, magic items were everywhere — +2 swords in goblin chests, potions on every corpse. 5e assumes scarcity, so too much gear can overpower your players fast.
Solution:
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Cut total treasure by 25–50%.
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Replace weaker magical items with flavorful story rewards (favor from a god, land deed, ancient secret).
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Keep iconic items (like the Sunsword or Blackrazor) but use modern mechanics.
6. Modernize the Flow
Old modules often assume the DM is adversarial and players are cautious dungeon crawlers. Modern groups tend to favor story and momentum.
Consider trimming endless empty corridors or repetitive fights, and focus on:
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Meaningful choices.
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Strong NPC motivations.
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Consequences that ripple through the adventure.
Add a few roleplaying scenes where classic modules are purely mechanical — it’ll feel fresh without losing the old-school charm.
7. Update Maps and Handouts
You don’t need to redraw every map, but modernizing them helps immersion.
Try:
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Using online map tools or grid overlays for virtual play.
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Scanning and cleaning old blue maps for print.
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Adding a few descriptive notes or dynamic lighting effects if you use platforms like Roll20 or Foundry.
Old dungeons can look stunning when upgraded visually.
8. Keep the Tone — That’s the Real Magic
Every classic module has a mood.
Keep on the Borderlands is frontier adventure.
Tomb of Horrors is a deadly puzzle box (and most of the traps can be solved with an abundance of chickens or a 10 foot pole).
The Lost City is strange and dreamlike.
Preserve that mood above all else.
Your players may be rolling 5e dice, but if the atmosphere feels authentically old-school, you’ve succeeded.
9. Add Hooks and Motivation
Earlier adventures sometimes dropped players in with little context: “You arrive at the dungeon entrance.”
Give modern players a reason to care:
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A personal connection to an NPC.
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A mystery to solve.
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A prophecy or relic tied to their backstories.
A few sentences of motivation can turn a random dungeon crawl into an epic quest.
10. Document and Share Your Conversion
Once you’ve successfully run your version, write it up!
DMs love seeing how others modernized old adventures.
Include:
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What you changed.
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What worked.
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What nearly killed everyone (in the best way).
It keeps the spirit of the classics alive — and helps other DMs keep the torches burning.
