Underground Cave

Lore & Background

In the lore of the RimWorld setting, underground systems have historically been used by those seeking to hide from the harsh realities of post-scarcity collapse. While ancient civilizations may have utilized deep caverns for industry or refuge, modern colonists often treat them as extensions of their base infrastructure. The darkness below is both a shield and a prison; it blocks out the screaming storms above but demands constant vigilance against the psychological toll of isolation. The geology of these caves varies wildly depending on the surface biome, yet they share a common trait: silence. Without wind or rain, the only sounds are the drills of miners and the scuttle of cave crickets. This isolation makes them ideal for high-value storage or secure prisons, though colonists must be wary that digging too deep can uncover unstable ground or ancient threats lurking in the dark.

In Their Own Story

The drill bit sparked against the granite wall as Kael adjusted his headlamp. Above him, a thunderstorm raged, shaking the surface soil, but down here, the air was still and cool. He paused to check his oxygen meter, then looked at the glowing blue mushrooms sprouting near the tunnel entrance. It was quiet, too quiet. Then he heard it—the distant scrape of metal on stone from the next cavern over. Someone else was digging.

Reader's Guide

The Underground Cave offers a unique environmental advantage: complete immunity to surface weather patterns. Rain, snow, and extreme heat never penetrate the deep stone, maintaining a consistently temperate climate year-round. This stability allows for reliable farming without seasonal disruptions, provided artificial lighting is installed to replace the absent sunlight. Resources here are abundant but require effort to extract. Walls consist primarily of hewn stone, while metal ores appear frequently in deeper veins. Flora is limited to hardy cave mushrooms, which thrive under electric lamps rather than solar radiation. Fauna includes harmless glowflies and edible crickets, though larger predators may occasionally wander into tunnels from the dark. Strategically, caves provide excellent defense against raiders due to chokepoints at entrances. However, colonists must manage darkness carefully; without sufficient light, mental breaks can occur among pawns who fear the dark. Mining operations expand usable space but risk accidental tunnel collapses or opening paths for unwanted visitors from neighboring underground networks. Proper ventilation is also required to prevent toxic gas buildup in sealed chambers.

Did You Know?

• Cave mushrooms do not require sunlight to grow if artificial light is present.
• Surface weather events like rain or snow never occur inside cave biomes.
• Glowflies emit a faint natural light but are insufficient for crop farming.
• Raiders can follow mining tunnels to breach underground colony defenses.