Demonreach

Demonreach is the name Harry Dresden gave to an island in Lake Michigan. The island first appears in Small Favor.

Description
Demonreach is an island in Lake Michigan that was removed from maps after a long association with the supernatural. The energies around the lake deter travellers from approaching and slowly become hostile to those who approach.

In Cold Days, it is revealed that the island's magic was created and placed by the the Original Merlin across time as a supernatural prison to keep the worst and most powerful evil beings contained. There are half a dozen naagloshii imprisoned there; these are considered the most benign, low-security inmates. Other entities, described as "[n]ightmares, dark gods, nameless things, immortals" are also imprisoned there. (ref?)

The island was once the location of a cannery in the early 1900s, until the magic from what Harry Dresden believed to be a ley line running through the island killed enough of its inhabitants to chase them away. It is later revealed that the ley line does not run through the island, but from it; the island, particularly the supernatural prison far below it, is the source of the ley line's tremendous power. The Gatekeeper Rashid has advised Harry not to use that power directly, only the Intellectus of the island's spirit.

Harry is currently the Warden of this prison, a duty he inadvertently took on when he performed the Sanctum invocation and bound himself to the island.

Harry describes it as covered in woods, lots of trees under a foot in thickness. Between the trees there is brush and thickets with thorns growing about five feet up from the ground. There is an old ghost town along the shoreline so old that trees have reclaimed the space and most of the buildings have fallen down. There are the rotting remains of an old dock with only the posts sticking out the water. Up on the highest point of the island on a hill stands the outline of a worn building or tower.

In Turn Coat, Harry Dresden uses the Sanctum Invocation on the island and its genius loci. He names it Demonreach. With Thomas' help, he constructs a floating dock, which they name "Whatsup Dock".

The island is known at some point to have had some sort of conflict with Senior Council member and Gatekeeper Rashid.

The stones on the cottage and on the tower glow with fox fire, then evolve into symbols, script in some unknown language. They seem to repulse the naagloshii, keeping him from approaching the structures. Bob tells Harry that he doesn't know what the symbols on the rocks of the cottage are except that they predate wizardry and are very powerful and very numerous—hundreds on each rock—and layered.

In Cold Days, Harry stated that the spirit entity of Demonreach spoke to him at Graceland cemetery, the year before.

Genius Loci
The island's genius loci is an extremely old and powerful one. It has Intellectus confined to its shores, which Harry Dresden is able to use while on the island. Demonreach's genius loci manifests as a tall figure—about eleven or twelve feet tall—with a billowing black cloak, a limp (caused by the glacier that carved out the lake), and two vividly green eyes.

As a very old genius loci, Demonreach contains considerable power. In Cold Days, the manifestation of the island manages to resist the power of Maeve, the Winter Lady (one of the most powerful Sidhe), and a retinue of high ranking Sidhe Nobles, while simultaneously warding off an attack from an army of outsiders. It took the combined powers of both Ladies and their retinues hours to even damage him slightly, a testament to his immense power.

However, Demonreach seems limited in its ability to actively resist invaders, which Harry speculates is due to the nature of the island itself. Mab acknowledges that Demonreach could have responded more aggressively to her daughters' attack and thanks him for being restrained.

Small Favor
In Small Favor, the Denarians took Marcone and The Archive hostage and brought them to the island. Harry, Michael, and Sanya go there with an agreement to trade eleven Denarian Coins and Fidelacchius for Ivy. The island feels familiar to Harry, though he's never been there before. The trade turns into a rescue and chaos breaks out.

Turn Coat
In Turn Coat, Harry Dresden uses the Sanctum Invocation on the island and its genius loci. He names it Demonreach.

Morgan is falsely accused of murder, and Harry invites all the parties of interest to witness his solution to the mystery: Shagnasty, Lara Raith, the White Council... and hopefully the traitor.

Ghost Story
In Ghost Story, Harry Dresden's body is kept alive through a mixture of Queen Mab's power and Demonreach embedding vines into Harry's body to feed him nutrients until he can return to life and resume his position as the Winter Knight.

The statue of Eternal Silence that speaks to Harry in Graceland cemetery is probably Demonreach. Harry recognizes it later on, in Cold Days.

Cold Days
In Cold Days, Molly tells Harry that she and Lea think that the island will blow up in the next couple of days, taking a large chunk of the Midwest with it. Harry takes Bob to the top of the hill, where there is a fire waiting for Harry in the cottage. Bob tells Harry what little he knows about the symbols on the rocks of the cottage. Demonreach bids Harry and Bob to follow him down into the deep-deep well. Imprisoned there are six Naagloshii and numerous dark entities. Harry finds that he's now the Warden of this supernatural prison. Bob translates for Demonreach by creating a movie of how The Original Merlin constructed the prison by repeating the spell at the same place at different times but at the same time.

Harry has a parasite in his head that's causing him headaches; it helped keep him alive while his spirit wandered. Its price was that Harry not be told any details about it. Eventually it will burst out of his skull and kill him.

Maeve and Lily tell Harry that Mab has gone mad and plans to unleash chaos on the world that night—Halloween. Harry and team try to determine who is behind the spell required to release the monsters, and if it's Outsiders, who let them into this world. Though the Ladies can't lie, they could be wrong.

Harry leads the Wild Hunt, including the Erlking and Kringle, into battle with Outsiders on barges and numerous other boats led by Sharkface—He Who Walks Before—along the shoreline of the island. Harry leads his team up the hill, but a beautiful Circle that forms a wall of deadly power. Being part of the Island's architecture, only Harry can pass through. Inside, Harry finds Maeve and Lily trying to destroy the Demonreach entity using the island's Circle of Power. Fix and Harry engage in battle, and Harry uses the island's Intellectus to easily win. Harry and Fix join forces to stop Maeve.

Skin Game
In Skin Game, Harry jokingly calls the island spirit "Alfred", after Batman's servant. The Island's spirit appears to want the name, so Harry officially dubs it Alfred Demonreach.

Harry also notes that he's much more familiar now with the Island's defenses and how to use them, and he would have no trouble defeating even Sharkface in a rematch, if it were held on the Island. Harry becomes so comfortable on the Island that he forgets how spooky and hostile it normally seems to others, and wonders why his friends don't come visit often.

Word of Butcher
Per Jim Butcher, "(Rashid) has been on the island a couple of times, and it’s never gone well."

External references

 * Satellite Photo: File:Lake Michigan Landsat Satellite Photo.jpg - Wikipedia
 * Lake Michigan - Wikipedia
 * Lake Michigan - Google Maps