Crossing the Dungeon Rubicon

— Thomas Allom, 19th century

A rubicon, as in “crossing the Rubicon,” signifies a point of no return. It’s a staple of many enduring myths and appears as several “thresholds” in the monomyth as described by Joseph Campbell.

The rubicon bears particular significance in relation to the underworld. I’m most familiar with the katabasis of Greek myths, but many cultures have stories about passages to the underworld. I’ve seen examples in Scandinavian folktales, and the ancient Maya believed some cenotes led to Xibalba, the “Place of Fright.”

You may be familiar with the idea of the dungeon as a mythic underworld, described by Jason Cone as follows:

[A megadungeon] is an underworld: a place where the normal laws of reality may not apply, and may be bent, warped, or broken. Not merely an underground site or a lair, not sane, the underworld gnaws on the physical world like some chaotic cancer. It is inimical to men; the dungeon, itself, opposes and obstructs the adventurers brave enough to explore it.

In OSR games, dungeon exploration involves unique procedures, a
“zoomed-in” time scale, and close scrutiny of environmental details. The dungeon is distinct not only as an environment, but as a play experience. A rubicon can serve as a physical manifestation of this divide, emphasizing the transition from one mode of play to another, lending spectacle to the descent into the dungeon, and evoking wonder and trepidation.

What’s a more exciting way to enter a dungeon: strolling a few paces into a cave or canoeing two miles down an underground river?

A Practical Purpose

A rubicon not only serves a thematic purpose, but a practical one, too. Crossing a rubicon should require time, vulnerability, or resources—ideally all three. It should demand a tangible commitment to peril at the start of each delve.

The risk-reward balance of dungeon exploration begins to break down when characters can enter and exit the dungeon at their leisure. Traditionally, the wilderness serves as a barrier to the dungeon; characters arrive with finite supplies after a perilous journey.¹ However, not every campaign emphasizes wilderness travel. One-shots often begin at the dungeon. And some dungeons are nearby—or even within—settlements.

Consider designing a rubicon entrance that imposes a cost to accessing the dungeon and hampers retreat.²

Example: A Literal River

As you may know, the idiom “crossing the Rubicon” refers to a river. A wide underground river would make a great dungeon rubicon. Maybe corpses wash up on shore or get wrapped around boulders midstream. There definitely isn’t a boat down there. Characters probably have to wade across. The river is cold and chest-deep with slippery rocks strewn across its bed. Anyone who slips while wearing armor or a pack is finished. Characters will need to remove their armor before crossing. Getting equipment across (especially torches, spellbooks, and anything else that must stay dry) requires party members on either side of the river.

Example: A Gluttonous Maw

The way into the dungeon is through the mouth of a massive stone head. Characters must present a sacrifice to pass: one hundred pounds of freshly cooked and seasoned meat to enter, three amphoras of wine to leave. Something will eventually steal the wine if characters don’t bring it with them, hide it, or bury it.

Example: A Sea Cave

A long narrow passage, flooded except for a few hours during low tide. Characters must crawl through on their hands and knees and even on their bellies in places. This takes at least twenty minutes—an hour with a full pack. Better read that tide chart carefully!

Example: A Sinkhole

Deep enough that the rappel must be done in two stages: first to a ledge, then to the bottom. It takes half an hour to descend but two hours to ascend. It’s only safe to do so at night when the stirges that roost here are out hunting.

Advice

• A rubicon may introduce the theme of the dungeon or level.
• Crossing a rubicon should leave the characters vulnerable and exposed in a way that makes the players a bit uneasy.
• A rubicon may restrict ingress and egress to certain times.
• The more a rubicon hinders retreat, the more available other exits should be.
• The rubicon itself should not be dangerous—at least, not unavoidably so—but should demand a tangible commitment to peril, such as spending a minimum amount of time in the dungeon.
• A rubicon may offer one-way access to a dungeon or level, and this may even be desireable—provided players know this.
• A rubicon may limit what characters can bring with them.
• A rubicon may provide clues to how the underworld breaks the rules of the overworld.
• A rubicon doesn’t have to be the first room of the dungeon.

That’s it! Not every dungeon needs a rubicon, but I think most would benefit from one. My first-ever blog post, “100 Dungeon Entrances” includes entries that might make good rubicons, so consider checking that out.

1. Of course, characters can travel with a retinue of mercenaries and camp attendants if they can afford their wages. However, in old-school D&D this involves a new set of risk-reward considerations. The evasion rules amplify the risk of travel for a large party. While a party of four characters evade a group of four or more creatures 90% of the time, a party of 25 has only a 35% chance to evade a group of 31 or more creatures. (D&D Expert Rules, page 23). When the wilderness encounter table includes groups of 10–60 goblins or orcs, travel as a large party bears serious risk. ↩︎
2. Castle Kelpsprot, an original megadungeon I’m running, features rubicons between levels but not at the entrance. There are good reasons for this: it’s an open table game, so characters need to get into the castle, explore, and get out again in less than two hours of real time. However, the fact that they’re rarely more than a hundred yard dash away from safety diminishes the tension and magic of exploration. ↩︎