Labyrinth (#) is a type of site, functioning identically to a lair. It consists of narrow tunnels and a treasure room. Each labyrinth is home to a minotaur, who will aggressively defend the treasures.
A labyrinth can be discovered in adventurer mode either by travelling or by asking local people about the beasts. As you explore the labyrinth, the Minotaur will taunt you ('I'll grind your bones into porridge!' 'I'll eat you whole!') until you find and kill it - or it kills you.
A map of a typical labyrinth.