Critical Infrastructure

This is part 2 of a 3-part series about designing dungeons and underground structures in accordance with real-world conditions. This part explores the effects of water on underground structures, as well as the design of features like stairways. To explore the structural integrity of such structures, see Part 1 here. For practical advice for game masters and worldbuilders, see Part 3 here.

V. Vertical Space: Stairs, Shafts, and Multi-Level Dungeons

Vertical movement is where many fantasy dungeons quietly abandon all structural logic. Perfectly straight shafts plunge hundreds of feet downward. Stairs descend in neat, stacked layers as if gravity and geology were afterthoughts. In reality, vertical space underground is difficult, dangerous, and expensive—and those difficulties are exactly what make believable dungeon layouts more interesting.

Straight vertical shafts are rare in real underground construction because they are hard to excavate, hard to stabilize, and extremely unforgiving if something goes wrong. The deeper the shaft, the greater the pressure on its walls, and the more catastrophic any collapse becomes. When such shafts do exist, they usually serve a very specific purpose: ventilation, access to a mine face, or waste removal. In a fantasy dungeon, a long vertical drop should immediately raise questions about how it was carved, how it was used, and why it hasn’t failed yet.

More common are solutions that wrap vertical movement around solid material rather than cutting straight through it. Spiral staircases carved around a central core preserve a massive column of untouched rock to carry load. Sloped ramps and switchback tunnels reduce sudden changes in pressure and make excavation and transport easier. These approaches are slower and less dramatic, but they are far more plausible—and they naturally create choke points, sightlines, and defensible positions.

Multi-level dungeons also benefit from thinking in layers rather than floors. In the real world, underground construction often follows geological strata. Builders take advantage of stronger rock layers, avoid unstable seams, or stop entirely when conditions worsen. Translating this into fantasy design explains why dungeon levels might vary dramatically in shape, ceiling height, or structural integrity as depth increases.

Different levels can also reflect different construction eras. An upper level might be carefully engineered, with stone arches and regular supports, while deeper sections are rougher, narrower, or partially collapsed as techniques changed or resources dwindled. Each vertical transition becomes a point of narrative significance rather than just a change in encounter difficulty.

From a gameplay and storytelling perspective, vertical constraints are a gift. They justify ladders instead of staircases, narrow shafts instead of grand halls, and dangerous descents that feel earned rather than convenient. They also create natural bottlenecks and escape routes that make combat and exploration more dynamic.

When vertical movement respects structural reality, it stops feeling like a map gimmick and starts feeling like a consequence of the environment. Every step downward feels heavier, more oppressive, and more deliberate—which is exactly how going deeper into a dungeon should feel.

VI. Water Is the Real Final Boss

If there is one force more relentless than gravity in underground spaces, it is water. Stone cracks, wood rots, metal corrodes—but water exploits all of it. In the real world, water is responsible for more underground failures than dramatic cave-ins ever are, and fantasy dungeons should be no exception. In fact, most long-abandoned dungeons should be defined by their relationship with water.

Water gets underground in many ways. Rain percolates down through soil and fractured rock. Groundwater flows laterally through porous layers. Seasonal flooding raises water tables. Even humidity alone can slowly degrade materials over time. A dungeon does not need an underground river to have water problems; it only needs time.

Real underground structures are designed with this inevitability in mind. Floors are rarely perfectly flat—they slope gently toward drains or sumps. Channels are carved along walls to guide seepage away from occupied spaces. Cisterns collect water for controlled use, while less important areas are sacrificed to dampness or flooding. Where this management fails, decay accelerates.

This has enormous implications for fantasy worldbuilding. A dungeon that is centuries old and completely dry is the exception, not the rule. More believable spaces are cool, damp, and uneven. Moss creeps along walls where moisture lingers. Salt stains and mineral deposits mark old water paths. Wooden elements swell, warp, or rot away entirely. Metal fittings are pitted and fragile.

Water also reshapes dungeon layouts over time. Corridors become impassable as floors erode or collapse into softened ground. Lower levels flood and are abandoned. New routes are carved to avoid persistent leaks. What began as a clean, rational design turns into a patchwork of workarounds and failures. This organic degradation gives dungeons a sense of age and struggle that no amount of decorative lore can replace.

From a gameplay perspective, water is an incredible tool. It explains why certain areas are inaccessible, why creatures congregate in specific zones, and why some spaces are hazardous even without monsters present. Slippery floors, sudden drop-offs hidden beneath murky water, or slow-rising floods add tension without needing elaborate mechanics.

Perhaps most importantly, water reinforces the core theme of structurally sensible dungeons: survival is ongoing. A dungeon that still functions has either been actively maintained, cleverly designed to manage water, or blessed with exceptionally forgiving geology. Everywhere else, water is quietly winning—and the dungeon bears the scars.

VII. Materials Matter

Not all stone is created equal, and neither are the structures built from it. One of the fastest ways to make a dungeon feel more believable is to think about what it is made of—and what those materials imply about the builders, the environment, and the dungeon’s current condition.

Different types of stone behave very differently underground. Hard, crystalline rocks like granite can support wide spans and resist erosion, making them ideal for large chambers or deep construction. Softer stones like limestone or sandstone are easier to carve but more vulnerable to water, cracking, and long-term deformation. A dungeon cut into soft rock should feel more fragile: thicker walls, closer supports, more collapses, and more ongoing maintenance. If you want a massive underground hall, the surrounding geology needs to justify it.

Construction method matters just as much as material. A dungeon carved directly from bedrock will feel very different from one built out of masonry. Cut stone blocks and brick introduce joints, mortar, and seams—each a potential point of weakness where water can enter and stresses can concentrate. High-quality masonry implies skilled labor, time, and resources. Poorly fitted stone suggests haste, decline, or builders working beyond their expertise.

Mortar is an especially useful storytelling detail. Fresh, intact mortar indicates recent repair or continued occupation. Crumbling or missing mortar points to age and neglect, even if the stones themselves remain intact. In many real ruins, the stone outlasts the material holding it together, and the same should be true in fantasy dungeons.

Age and maintenance leave visible marks. Cracks widen slowly over centuries. Arches sag as materials creep under constant load. Wooden supports rot or are replaced with mismatched reinforcements. A dungeon that has been patched and repatched over generations feels lived-in and precarious, while one that has never been repaired feels either newly built or unnaturally preserved.

Magical materials and construction techniques can exist without breaking plausibility, but they work best when treated as rare and intentional. A magically reinforced ceiling should stand out, not be the default. Its presence should raise questions: why here, why this room, and what was important enough to justify the cost? Magic that replaces engineering entirely removes tension; magic that supplements it enhances both realism and wonder.

By paying attention to materials, you turn dungeon structure into character. The stone tells you how hard this place was to build, how long it has endured, and how close it might be to failure. Even without explicit exposition, readers and players can feel the difference—and that texture makes the dungeon far more memorable.

VIII. Ventilation, Smoke, and Airflow

Air is easy to forget in dungeon design because its absence is invisible—until it isn’t. In real underground spaces, air quality is a constant concern. Without deliberate airflow, smoke lingers, oxygen drops, and spaces become uninhabitable long before they collapse. If a dungeon is meant to be occupied, used, or even frequently visited, it must breathe.

Ventilation underground rarely relies on a single opening. Instead, it emerges from networks of shafts, secondary tunnels, cracks, and elevation changes that allow air to move naturally. Warm air rises, drawing cooler air in behind it. Even small differences in height between entrances can create steady circulation. This is why many real tunnels have vertical shafts that serve no obvious purpose other than letting air move.

In fantasy dungeons, ventilation explains a great deal about layout. Vertical shafts suddenly make sense. Multiple entrances aren’t just conveniences; they are necessities. Long, dead-end corridors tend to have poorer air quality, while frequently used spaces are positioned where airflow is strongest. If torches are commonly used, soot stains should accumulate on ceilings and near ventilation paths, subtly marking where smoke was able to escape.

Poor ventilation leaves clues as well. Stale, heavy air suggests disuse or blocked shafts. Blackened stone implies generations of smoke with nowhere else to go. Certain creatures—fungi, insects, or things that thrive in low-oxygen environments—naturally congregate in poorly ventilated sections. These environmental details make the dungeon feel reactive rather than designed purely for encounters.

Ventilation also reinforces hierarchy within the dungeon. Important areas are given better airflow and safer conditions. Storage tunnels, prisons, or sacrificial chambers might be intentionally placed where air is scarce. Over time, collapses or neglect can reverse this logic, leaving once-grand halls choking while forgotten passages breathe freely through newly opened cracks.

From a design perspective, airflow is a subtle but powerful guide. It justifies why some paths are more traveled than others and why certain areas feel oppressive even without obvious threats. A dungeon that manages air thoughtfully feels inhabited, engineered, and constrained by reality—even when filled with magic and monsters.

By remembering that underground spaces need to breathe, you add an invisible layer of structure that players and readers instinctively understand. The dungeon stops feeling like a sealed box and starts feeling like a living system—one that can fail quietly, long before the walls ever come down.

Dungeons That Make Structural Sense: Design and Water