Curse of the Crimson Throne
Most cities have sewers. Some can even claim dungeons and deep caverns beneath them. No city, though, has a complex system of subterranean tunnels quite like Korvosa, which stands atop the remains of at least two other civilizations.
The Shoanti who dwelt on the site long before its Chelaxian colonization dug squared ditches into the earth to bury their honored dead. Centuries later, Chelish settlers slowly connected many of these trenches, paying their dwarven allies to dig tunnels between them all. Without any regard to the dead Shoanti buried there, the Korvosans then made these tunnels into sewers. Today, the sewers under much of mainland Korvosa make little sense, making random turns and possessing numerous festering dead ends, thanks to the haphazard layout of the Shoanti burial mounds.
Korvosa is also blessed with a large number of natural caves, some hollowed out by the sea, others produced by volcanic action. These irregular caverns and caves delve deep beneath the surface of the earth, sometimes well beneath the water table.
Many of the deepest tunnels and chambers beneath Korvosa bear the unmistakable mark of the city’s first inhabitants, the powerful but decadent ancients of lost Thassilon. It is rumored that some of these hidden Vaults contain powerful relics and vast riches, though most hold only disappointment and danger for would-be explorers.
With such a sprawling network of tunnels and caverns, the sewers and vaults of Korvosa have developed into a habitat for many sinister creatures. The city has released a number of otyughs into the sewers to help control waste, especially in Old Korvosa, whose sewer system is disconnected from the mainland. The abominations compete for food and territory with wererats, tunnel terrors, and other, fouler things in the stinking depths below the city.