Lundy Island, is the largest island in the Bristol Channel. It also hides the Fourth Vertex.
While researching the location for the Second Vertex, Lachlan Adamson noted how the third corner of a triangle he'd created to link Stonehenge, the neolithic stones and the Great Pyramid touched upon Lundy Island, but was distracted from further investigation.
After the final Pillar was placed at the Sixth Vertex, the Fourth Vertex beneath Lundy Island activated once again. This time, as the beam of light it emitted struck the Earth's iron core, it was accompanied by the light beam ignited from the other five Vertices, causing a series of harmonic waves that repelled the Dark Sun.
The Fourth VertexEdit
The Fourth Corner of the Machine, the City of Waterfalls, is located beneath Lundy Island. Like every other Vertex, there is the inverted pyramid of the Machine, which is set above a seemingly bottomless chasm. The 'city' is a set of ledges within the Vertex's cavern, and there is a viewing platform on a side wall to the entrance. The people on the platform must guide their allies through the maze of ledges, using the transcribed safe route from the plaque describing each Vertex. This forces the Pillar setters to beat the rushing water entering the cavern at the time of the Titanic Rising.