The Tunnels under Corunglain

“Despite all the precautions which the city guards take against attacks and raids by the inbabitants of the Broken Lands, they seem unable to prevent small bands of them from sneaking into the city. It is believed, though proof is hard to come by, that the earth beneath Corunglain is honeycombed with a twisting maze of passages. If, as is believed, this labyrinth links up with the orc tunnels beneath the Broken Lands then the actions of the raiders are easily accounted for. By moving though the passages which are narrow and prone to periodic collapses, small bands of orcs, goblins and their kin can appear in the city, wreak a little havoc and then melt back into the earth without leaving a trace. 

The government of Corunglain has uncovered many openings which, they believe, lead into this underworld. In each case a demolition team has collapsed the passages and the discoverer given a substantial reward. It is certain that, given time and effort, a dedicated band of adventurers would be able to find additional entrances to the orc tunnels and earn the thanks of the local populace.”

Gaz11 The Republic of Darokin, DM’s book p36

And thus a mini-campaign for novice adventurers is established. Personally I really like this idea, as it means the adventurers are less like bandits themselves, raiding and slaying the humanoids, but actually defending the city from infiltrators. This has similarities with B2 The Keep on the Borderlands (going against various bands of chaotic humanoids) but set in a major city of 31,000 folks instead of a keep with a hundred or so inhabitants. 

This map shows the layout of the tunnels under Corunglain and shows what is underneath the map in this post about the surface of Corunglain. 

As can be seen there are numerous tunnels reaching all the quarters of the city. Note that this map could be just the uppermost level of tunnels - there could be even more deeper underground, and could even be part of a megadungeon. There are a dozen small lairs of three to six chambers each attached to the tunnels - this is where the humanoids rest, prepare for raids, count loot and store weapons and food. Each of these lairs is run by a gang of humanoids, usually a single race. 

There are also tunnels leading away from the city - these are the highways along which the humanoids will travel great distances. It is believed from interrogating captured goblins that there are waystations every 10 miles or so where humanoids can rest and eat. Supply wagons with food, weapons and fresh recruits can be encountered here as well as the occasional messenger. 

The tunnel complex shown here is above the water level of the river and wells, with some of the tunnel entrances opening out outside the city walls onto the river bank or a ledge on the cliffs overlooking the rivers. Only when the tunnel goes under the river does it slope down much further. At least one lair (the bottom right one) connects straight to a well shaft, about 20ft above the water level. The kobolds lodged there have learnt how to climb up the wellshaft into the surface city. 

The tunnels are all left dark, since goblins, kobolds, orcs and hobgoblins all have infravision so can see just fine. Of course these races all prefer the darkness anyway - sunlight is irritating and makes them nauseous.  In fact any light source will indicate human intruders to sentries. The tunnels are generally under 6ft tall so gnolls, bugbears and ogres rarely visit as they would have to stoop down all the time. The human soldiers who have to fight these humanoids are actually very grateful for this restriction.  

The humanoid raiding parties are usually single race, e.g. all kobolds or all goblins, and will typically be 6-10 individuals, led by a tougher, smarter warrior who acts as squad leader. There have been a few occasions of mixed-race raiding parties but these run the risk of rivalries and friction between the races.  The hobgoblins see themselves as the bosses of this tunnel complex and often stop any inter-humanoid fights getting out of hand - the hobgoblins remind everyone that the real enemies are the humans above. 

The big exception to segregation is the large chamber in the north, underneath Cheesemarket Square (#16). This is known as the Gathering Hall and is used as a neutral meeting ground and muster point, as well as a common point for those travelling along the main tunnel to the Broken Lands. Interestingly enough some goblins and hobgoblins have started to imitate the humans of Darokin and have set up market stalls in the Gathering Hall, selling things that goblins, orcs and kobolds might want to buy - roasted rats on a stick, stolen weapons, strong beer, makeshift armour and the occasional kidnapped human. Although the stall owners are unlikely to trade with humans or demihumans, adventurers magically disguised as humanoids could buy things here. One gnome trickster claims to have visited the Gathering Hall several times and even considered setting up shop disguised as a paunchy kobold, but decided it was too risky and too smelly. 

What do the raiding parties get up to? Theft, Murder, Kidnapping, Vandalism, Sabotage, Espionage and scaring the humans. Sometimes these are with a bigger goal in mind, to destabilise the government, terrorise the population and demoralise the army, but usually it is much more small-minded, doing it for food, money and fun - that’s what humanoids are like. Some humanoids join these raids for social standing within their tribes - a warrior who brings back food, loot and slaves to their lair will be seen as more valuable and a potential leader by other members of the gang. 

It is rumoured that some goblinoid leaders are considering a major assault through these tunnels, with bands emerging simultaneously from different tunnel entrance. Espionage was mentioned above because some senior tribal leaders back in the Broken Lands are interested in what the city garrison’s response times are, and who else would oppose the humanoids. The humanoids already have a pretty good map of the city and already know the best routes to and from the tunnel entrances. But given the number of human soldiers stationed in Corunglain the humanoids would probably need twice as many on their side to succeed in overrunning the city. A more realistic prospect is combining an overland assault from the Broken Lands with raiders emerging within the city to distract the garrison and maybe open up the gates or lower ropes down the outside of the city walls

The city’s responses to these raids are with either the army or adventurers:

The XIII legion based in the Bastion includes the Corunglain Combat Engineers Company, also known as the Underminers. They can call upon some friendly mages for support and while the combat engineers provide protection, the mages will cast Wall of Stone or Rock to Mud to seal off tunnels and entrances.  The combat engineers do know of mundane ways of sealing tunnels if mages are not available, but these methods are slow and humanoids may counterattack while the engineers are working. 

Sometimes the army or city council will ask the Adventurers’ Guild to hire some suitable heroes to deal with the problem, especially if fighting underground is expected - the army is better suited to combat in large formations on open fields or city walls. This is particularly likely if the humanoids are believed to have seized captives who need rescuing or valuable items that the leaders of Corunglain want to retrieve - simply collapsing the tunnel is not appropriate. 

Unintelligent monsters, particularly giant rats, giant bats and giant crab spiders are a perpetual nuisance, and the hobgoblins may bully the smaller races into dealing with these vermin before they get out of hand. Nonethelss at least one lair has been taken over by vermin, displacing or killing the previous goblin residents. Corunglain does not have a proper sewage system so at least there are no otyughs to contend with. One arrogant hobgoblin chief brought along his pet carrion crawler - it paralyzed and ate him, then escaped into the tunnels. There are rumours among the tribes and gangs that it is still alive, lurking in the dark corners of the tunnels.

The lich Meltherrion is a potential disaster for anyone who encounters him, though diplomatic and respectful humans should escape with their lives.  This could be a valuable lesson for low-level adventurers - not every monster is there to be defeated in combat.  The known part of his lair is marked in pale pink on the map, though given the magical tools he has access to this is probably not the whole of his domain.  He does not like being disturbed but he really hates humanoids - as such he could be a powerful but unpredictable ally.