The tunnels are a mix of both artificial and natural passages that spread all over the island, including to, around, and under Verens, with most of the entrances within the city itself being hidden. They're a bit complex and are largely dark and damp thanks to a few entrances to the sewers, and anything that would sneak around underground can be found there, from rats to reptiles. There are also a few hints towards human activity, including lanterns and materials like rope and wood, although it's mostly quiet in there.