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Wednesday, December 2, 2020

The Ruined Tower of Zenopus: Running it Retro

Occasionally, I have been asked about a retro version of
The Ruined Tower of Zenopus (RTOZ); i.e., one for an old-school D&D or OSR ruleset. There is of course, the original adventure, still available as a free pdf on the Wizards site, but it doesn't include the content that I added. 

I would love to include such conversion notes in the adventure itself, but DMs Guild doesn't allow products to include rules for non-5e D&D systems. So instead I will post some notes here on the blog. These are written up for Holmes Ref, which uses OD&D to expand Holmes, but really should be sufficient for any old D&D (e.g., OD&D, B/X, AD&D 1E, AD&D 2E) or retroclone thereof. These notes focus on rules & assume that you have a copy of the RTOZ at hand.

Pages 1-3 don't require any retroversion. Page 1 is the cover; page 2 the introduction; and page 3 is my map of Portown and a description of the points of interest. No rules here!

Page 4

Doors: Force open on 1-2 in 6, optionally modified for strength (i.e., if using Strength adjustments for doors such as I included in the Rolling Up An Adventurer sheet for Holmes Ref or the bonuses given in the Greyhawk supplement). Repeat attempts are possible, but there is no chance for surprise after the first attempt. Doors can also be chopped apart with the right tools, such as axes; this takes 1 turn and makes such a racket that it necessitates an immediate check for wandering monsters.

Wandering Monsters:

Check as indicated; the rules given in the RTOZ are the same as in the original dungeon.

For the monsters, use the following stats. If running Holmes, you can use 1/10 of the MV as Dexterity for determining first strike, or roll it on the spot as suggested in the Holmes rules.

For HD, "NH" means "normal human". For Holmes, this means they have 1d6 hp and use on their own line on the combat and saving throw tables (which is -1 compared to a 1st level fighter). In OD&D, they would be treated as 1st level fighters.

The behavior and treasure for each monster can be left unchanged.

1. 1d3 goblins: MV 60, AC 6, HD 1-1, AT 1 weapon for 1d6

2. 1d3 zombies: MV 60, AC 8, HD 2, AT 1 claws for 1d8, only attack every other round

3. 1d3 skeletons: MV 120, AC 8, HD 1/2, AT 1 claws for 1d6

(Note: I use the Monster Manual move rates for zombies and skeletons, which is reversed from that of the Holmes rulebook. If you prefer, switch them back).

4. 1d6 giant rats: MV 120, AC 7, HD 1/2, AT 1 bite for 1d3 + 5% chance of disease

    1 monstrous rat: MV 180, AC 5, HD 1-1, AT 1 bite/1 claws for 1d3+1 each

5. 1d6 large sand crabs: MV 90, AC 6, HD 1/2, AT 2 pinchers for 1d4 each

6. 1d3 giant centipedes: MV 150, AC 9, HD 1/4, AT 1 bite for 0 but save vs. poison at +4

7. 1d6 smugglers: MV 120, AC 7, HD NH, AT 1 cutlass for 1d6

8. 1d3 large spiders: MV 60, AC 8, HD 1+1, AT 1 bite for 1 + save vs. poison at +2

9. 1d6 stirges: MV 180, AC 7, HD 1, AT 1 proboscis (at +2) for 1d3 & drain blood at 1d4/round

10. 1d6 cultists: MV 120, AC 9, HD NH, AT 1 scimitar for 1d6

11. 1 ghoul: MV 90, AC 6, HD 2, AT claw/claw/bite for 1d3 each & paralysis

12. 1 cleaning cube: MV 30, AC 9, HD 2, AT 1 touch for 1d4 & paralysis

Instead of an item from the 5E Trinkets table, the cleaning cube will be carrying a random piece of equipment from the Holmes Ref Equipment Reference Sheet


Holmes-style stat blocks are below. Use the descriptions from the RTOZ.

Monstrous Rat

Move: 180 feet/turn, 90 feet/turn swimming
Hit Dice: 1-1
Armor Class: 5
Treasure Type: Q
Attacks: 1 bite, 1 claws
Damage: 1d3 + 1 each

(I wrote this up previously as a "Giant Rat King" here)

Large Sand Crab

Move: 90 feet/turn
Hit Dice: 1/2
Armor Class: 6
Treasure Type: nil
Attacks: 2 pinchers
Damage: 1d4 each


Move: 120 feet/turn
Hit Dice: Normal Human (1d6 hit points)
Armor Class: 7
Treasure Type: 2d6 gp
Alignment: neutral
Attacks: 1 cutlass
Damage: 1d6


Move: 120 feet/turn
Hit Dice: Normal Human (1d6 hit points)
Armor Class: 9
Treasure Type: nil
Alignment: chaotic evil
Attacks: 1 scimitar
Damage: 1d6 

Cleaning Cube

Move: 30 feet/turn
Hit Dice: 2
Armor Class: 9
Treasure Type: variable
Attacks: 1 touch
Damage: 1d4 plus save vs. paralysis

Page 5: Doesn't need any retroversion as it is just a printer-friendly map of the dungeon.

That's it for now. I'll continue in another with notes on converting the rooms (Page 6 & beyond).

The second & final installment of "Running it Retro" can be found here.


  1. Have you considered Drivethru RPG? I thought it was affiliated to DM's Guild?

    1. One has to release material on DMs Guild to use their IP in an adventure. So to incorporate the material from the original adventure I could only release the Ruined Tower there.

  2. I ran this module using these Old School conversion notes for my group. It was very successful. Highly recommended.