Location from The Dresden Files by Jim Butcher
A haunted island in Lake Michigan that serves as Harry's sanctum — and as a prison containing hundreds of apocalypse-level supernatural beings, guarded by an ancient genius loci named Alfred.
Demonreach is a small, rocky island in Lake Michigan that most Chicagoans know vaguely as 'that island nobody goes to.' The trees are old and twisted. The shoreline is unwelcoming. The island radiates a psychic sense of wrongness that makes normal people feel uneasy and turn their boats away without quite knowing why. Animals avoid it. Fish don't swim near it. The island is, in every meaningful sense, alive. The genius loci — the spirit of the island itself — is an entity Harry named Alfred. Alfred is ancient, powerful, and absolutely literal-minded. He serves the Warden of the island, which is currently Harry, and he does so with the personality of a granite cliff: immovable, patient, and capable of terrifying violence when the island's security is threatened. Alfred can manifest as a humanoid figure of stone and shadow. He can extend the island's defenses. He can communicate the status of every prisoner in the Well. The Well is the real secret of Demonreach. Beneath the island, in crystalline cells extending down into the bedrock, hundreds of beings are imprisoned — entities powerful enough that their release would constitute apocalyptic events. Naagloshii, ancient demons, mad gods, things that don't have names in human languages. The prison has existed for millennia. Whoever built it — and even the White Council doesn't know who — designed it to last forever. Harry discovered its true nature almost by accident and now carries the responsibility of ensuring none of those things ever gets out. The island sits on a massive ley line convergence, giving it enormous ambient magical energy. Harry uses it as his sanctum, drawing on the island's power for workings that would be impossible anywhere else. It's also phenomenally well-defended — the island's defenses can sink battleships.
Rocky island in Lake Michigan, perpetually shrouded in cold mist. Twisted trees lean away from the center. The surface is unremarkable — dark stone, sparse vegetation, an old lighthouse. Below, miles of crystalline prison cells contain beings that could end the world.
Also known as: Demonreach, the island, the Well