Some hexes in both Thar and Vestitas are occupied by cities. These cities have far too much going on in them to be portrayed as a single encounter, but dungeon crawl mechanics rarely work for them. Even Chaos Landing in Vestitas is a dungeon attached to Brandt’s Landing, not the entirety of the content in Brandt’s Landing. Urbancrawls are how you find out about and subsequently solve whatever troubles a city is facing within its walls. We’re giving the D&D 5e version used for the Thar cities of Thentia, Hulburg, and so on, but the Dark Heresy 2 rules are very similar.
A city is divided into multiple neighborhoods. The characters can visit these neighborhoods anytime they want, at-will. Unlike in a hexcrawl or a dungeoncrawl, there is no process for traveling from one to another and there are no random encounters along the way. No appreciable amount of time passes while moving from one neighborhood to another. What does take an appreciable amount of time is looking for trouble.
Each neighborhood has at least one encounter in it, and each encounter has a DC for how hard it is to find. When characters go trawling for rumors or investigating problems nearby, they roll Investigation. The Investigation check is compared against the DC of the encounter with the lowest discovery DC in that neighborhood. If the characters’ Investigation check hits that encounter, they’ve found the hook, which will usually be some suspicious activity going on in more or less plain view (though not necessarily in an obvious way). If there are multiple encounters with the same DC, the GM can pick which one gets spotted. If the characters beat the DC by at least 5 points, they get another encounter, so long as they meet that encounter’s DC. For example, say a neighborhood has two encounters, both with a DC 15 Investigation check. The party rolls a 20 for their Investigation, so they discover the hook for both encounters. On the other hand, if the neighborhood has two encounters, one at DC 15 and the other at DC 25, they only get the DC 15 encounter’s hook. They’ve rolled an extra five points, so they get a second encounter, but their roll isn’t high enough to reach any of the encounters. Additionally, if there are simply no encounters left to discover, players do not get any extra encounters for beating the DC by a wide margin. If characters are searching for a specific encounter located in that neighborhood, or if they’re looking for a specific antagonist (for example, a thieves’ guild that they know is operating in the town), they get advantage on their Investigation check for knowing what to look for.
All encounters have a discovery DC, but for some it is extremely high, even impossibly high. A sufficiently paranoid villain can place themselves completely out of reach of investigation using layers of secrecy, having lieutenants carry out their nefarious schemes without ever directly participating. In this case, it’s more likely that players will find the encounter by interacting with those more easily discovered lieutenants’ encounters than by directly hitting a DC 35 Investigation check. It’s perfectly fine for players to go directly to an encounter without rolling if they’ve learned through organic play of the encounter’s existence and location. In fact, it’s preferable that, once they get a lead through Investigation checks, they generally don’t have to roll Investigation again for a long time, instead following the information from one encounter to another naturally.
Other encounters might have extremely low discovery DCs. If a part of town has been effectively taken over by a mercenary company who levies protection fees on the locals and kills the town guard if they ever set foot within the quarter, you really don’t need to be super perceptive to figure it out. It’s perfectly fine to have encounters whose discovery DC is 5 or even 0.
Related encounters, like a thieves’ guild or a vampire coven, are called a sub-plot. Sub-plots help keep things organized and makes it quick and easy to figure out which encounters are related to one another. Sub-plots may also react to player activity directed at them, for example, encounters within a sub-plot might be more guarded or have additional reinforcements if the characters have shut down a certain number of other encounters in that sub-plot. Sub-plot villains might start sending assassins or otherwise retaliating against characters while they’re in the city if the characters solve enough encounters. On the other hand, defeating one or a small handful of encounters who contain the organization’s leadership might cause the remaining encounters to flee or cease activity.
A single encounter can be in two sub-plots at once. For example, the lair of a vampire whose infiltrated the thieves’ guild could be in both the vampire coven and thieves guild sub-plots simultaneously.
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