Originally published in 1980 for 1st Edition AD&D, C1: The Hidden Shrine of Tamoachan is a perfect candidate for Castles & Crusades (C&C). Because C&C is built on the "Rosetta Stone" of the Siege Engine, it is largely compatible with 1E modules with minimal on-the-fly conversion.This picks right up from Aethel, the Sunken Core Inner Earth Sword & Sorcery Campaign Adventure Using both Castles & Crusades (C&C) and Night Shift: Veterans of the Supernatural Wars (NSW) Rpg- "The Weeping Monolith of the Silt-King,"
Here is the breakdown of how to run this Mesoamerican-themed "death trap" dungeon using the C&C ruleset.
1. The Core Challenge: The Siege Engine
The biggest shift from 1E to C&C is moving from "percentage chances" and "fixed saves" to Attribute Checks.
Traps & Hazards: Tamoachan is infamous for its environmental puzzles. In C&C, almost every interaction should be a Challenge Base (CB) check.
Example: If a 1E description says "1-in-6 chance to notice the pressure plate," use a Wisdom Check (CL 5-7).
Saving Throws: Convert 1E saves directly to C&C Prime/Non-Prime checks.
Poison/Gas: Constitution.
Dodge/Pit Traps: Dexterity.
Ancient Curses/Mental Stress: Charisma or Wisdom.
2. The Poison Gas Mechanic
The most iconic (and controversial) part of C1 is the amber-colored poison gas in the lower levels that slowly kills the party.
The Original Rule: 1d6 damage every 10 minutes (1 turn) with no save.
C&C Adjustment: This can be brutal for C&C’s flatter HP curves.
The "Gritty" Approach: Keep it as-is to maintain the tournament "ticking clock" feel.
The "Siege" Approach: Allow a Constitution Check (CL 5) every 30 minutes. Success means the character takes no damage; failure results in 1d6 damage and a -1 penalty to all physical checks due to coughing and nausea.
3. Monster Conversions
Most monsters in C1 have direct equivalents in the C&C Monsters & Treasure book.
| C1 Monster | C&C Equivalent | Note |
| Giant Crayfish | Giant Crayfish | Keep the "crushing" grapple mechanics. |
| Gibbering Mouther | Gibbering Mouther | Use a Charisma Save to avoid the confusion effect. |
| Nereid | Nereid / Water Nymph | Be careful with the "kiss of death"—it's a high-CL Con save. |
| Giant Slug | Giant Slug | Acid spit should target AC or require a Dex check to dodge. |
| The Vampire (Lozakan) | Vampire | In C&C, vampires are high HD. Scale the HD to match the party level (approx. 7-8 HD). |
4. Specific Mechanics to Watch
The "Tournament" Scoring
If you aren't running this as a competition, ignore the scoring system. However, the pre-generated characters are very well-balanced for the module's lethality. If your players are bringing their own characters, ensure they are at least Level 5–7.
Ancient Olman Lore
C&C emphasizes a "Classic Fantasy" feel. The Mayan/Aztec flavor of the Olman people provides a great opportunity for Intelligence (Legend Lore) or Wisdom (Religion) checks to decipher the murals, which often give clues on how to bypass traps.
Knocking/Breaking Doors
Many doors in Tamoachan are stone or heavy bronze.
CK Tip: Tamoachan is a "thinking player's" dungeon. Reward clever use of the environment. If a player uses a Strength (Athletics) check to wedge a stone block into a trap reset mechanism, give them a +4 bonus or automatic success to encourage that OSR-style play.
Integrating The Hidden Shrine of Tamoachan into an Inner Earth (Hollow Earth) sandbox campaign is a brilliant move. It shifts the dungeon from a "forgotten ruin" to a "gateway" or a "border fortress" between the surface and the subterranean world.
Here is how to adapt the module for a Hollow Earth C&C sandbox:
1. The Narrative Hook: The Descent
In a standard game, the players fall into the shrine. In an Inner Earth campaign, the shrine shouldn't just be a dead end; it should be a Vertical Transit Point.
The "Bottom" is the Top: Consider flipping the progression. The players might enter through a "sun-hole" in the jungle floor and realize that as they descend, the air pressure changes, the gas thins, and they emerge not into a basement, but onto a cliffside overlooking the Inner World.
The Olman as Gatekeepers: In your sandbox, the Olman civilization might not be extinct. They could be a thriving (or decadent) empire living on the "inner shell," and this shrine is their primary customs house or a forbidden seal preventing "outer" Surface-Dwellers from entering.
2. Environmental Adjustments
Running this in a "Dying Earth" or "Hollow Earth" context allows you to play with the atmosphere:
The Poison Gas (The Breath of the Earth): Instead of just being a trap, the amber gas could be a heavy, volcanic byproduct that pools at the "rim" of the Inner Earth.
Siege Engine Hook: Characters with a Survival or Nature background can make a Wisdom Check to realize the gas is actually a natural barrier meant to keep certain bioluminescent "Inner" bacteria from reaching the surface.
Gravity & Light: As the players reach the lower tiers (Rooms 39-54), describe the shift in gravity. Use a Dexterity Check (CL 3) to adjust to the "curve" of the world as they exit the shrine.
3. Faction Integration
Since this is a sandbox, the monsters shouldn't just wait in rooms; they should have connections to the Inner Earth.
| Creature/NPC | Sandbox Role |
| Lozakan (Vampire) | A disgraced "Border Prince" of the Inner Earth, exiled to the shrine to guard the exit. He may trade information for a way back in. |
| The Giant Crayfish | A common food source for the Subterranean Tribes. Finding its lair might lead to a hidden tunnel used by smugglers. |
| The Doppelganger | An advance scout for an Inner Earth "Deep Empire" (like the Drow or a reptilian race) trying to infiltrate the surface. |
4. Connecting the Map
To make this part of a sandbox, you need Exits that lead deeper into your campaign world:
The Water Pit (Room 42): Instead of a simple flooded room, this could connect to a massive "Inner Sea" or a series of hydrothermal vents that lead to an underground civilization.
The Pillar of the Sun: If the players restore the light here, it could act as a beacon visible from miles away within the Hollow Earth, attracting the attention of local factions (flyer-mounted scouts or nomadic tribes).
5. Loot & Lore: The "Inner" Connection
Replace some of the generic gold with items that have utility in your specific sandbox:
Olman Maps: Instead of just treasure, include stone tablets that map the "Inner Rim" of your world.
Sun-Gems: Replace standard gems with "Light-Stones" that glow with the frequency of the Inner Sun, essential for navigating the darker "crust-forests" below.
CK Advice: Since C&C thrives on exploration, treat the "Hidden Shrine" as a Level 1–3 Mega-Dungeon Entrance. If they survive the "Death Trap" gauntlet of Tamoachan, they earn their right to enter the more expansive, weird-fiction landscape of the Inner Earth.
Mixing a Prehistoric Lost World with High-Magic Alien Civilizations creates a fantastic "Sword & Planet" vibe for Castles & Crusades. In this version of the Inner Earth, the Shrine of Tamoachan acts as a "pressure lock" between the primitive surface and a technologically/magically advanced interior.
Here is how to blend those two aesthetics within the module’s framework:
1. The Aesthetic: "The Obsidian Tech"
To bridge the gap between Mesoamerican ruins and alien high-magic, replace stone with Obsidian Glass that pulses with circuit-like energy.
The Murals: They don't just show myths; they are holographic archives. A successful Intelligence (Legend Lore) check might trigger a projection showing the "Great Migration" from the surface to the Inner Earth during a prehistoric cataclysm.
The Light: Instead of torches, the shrine is lit by hovering Plasma-Orbs (treat as Continual Flame, but they can be "short-circuited" by electricity-based attacks).
2. Monsters: Bio-Engineered Horrors
The creatures in Tamoachan shouldn't just be "animals"; they are the mutated or engineered remnants of the alien civilization’s biological experiments.
The Giant Slug (The Bio-Purge): Describe it as a translucent, synthetic organism designed to "clean" the shrine's corridors of organic waste (like the players).
The Kopoala (The Feathered Ferocity): Instead of a standard bird/cat hybrid, make it a Deinonychus with iridescent, glowing feathers—a prehistoric predator "uplifted" with alien intelligence.
The Doppelganger: It’s not a shapeshifter; it’s a Nanite-Swarm taking a humanoid shape. In C&C, give it a +2 to its Armor Class because its body is semi-liquid.
3. The "Two Tiers" of Loot
In a sandbox, the rewards should reflect the two-sided nature of your world.
| Item Found | The "Lost World" Aspect | The "Alien Magic" Aspect |
| Macuahuitl | A masterwork obsidian-edged club (+1 to hit). | It vibrates at a high frequency, ignoring 2 points of non-magical AC. |
| Olman Headdress | Grants a +2 to Charisma checks with primitive tribes. | Acts as a Translation Matrix, allowing the wearer to understand alien dialects. |
| Golden Statues | Worth 500gp in surface markets. | They are actually Power Cells for ancient machinery found deeper in the Inner Earth. |
4. Expanding the Map: The "Vertical Sandbox"
Since this is an Inner Earth campaign, the bottom of the shrine (Level 1) shouldn't just be the end. It should be the Observation Deck.
The Exit (Room 54): When the players finally break through the final doors, don't have them emerge into a cave. Have them step out onto a high-altitude balcony carved into the side of a titanic stalactite.
The View: Below them is a sprawling jungle of giant ferns and bioluminescent fungi (The Lost World). Hovering above that jungle are Floating Ziggurats and crystal spires of the High-Magic civilizations.
The Travel: Next to the exit is a Gravity Lift (an alien platform) that can take them down to the jungle floor, but it requires a "Key of Tamoachan" found in the Vampire’s coffin to activate.
5. C&C Faction Play: The First Encounter
As soon as the players exit the shrine, they should be caught between your two worlds:
The Primitive: A hunting party of Pterodactyl-riding Olman warriors (use the Knight or Ranger class template for their stats). They view the shrine as a holy site.
The Advanced: A Silver Sentinel (a magical construct/golem) from the inner cities patrolling for "surface contamination."
CK Tip: Use the Siege Engine to handle the "Tech-Shock." If a character tries to use an alien device, have them roll an Intelligence Check. If they have a "Knowledge: Arcana" or "Engineering" background, they add their level. If not, the CL is much higher (CL 10+) to represent the sheer alien nature of the magic.
