The road on fire
Beneath the Knot, literally the flip side of the known hedge is an alien landscape lit by neon emanating from strange coral, algae and kelp that pulse green, yellow and pink against the abyss black backdrop. Legendary monsters stalk the Underside, swim just above it in the sky above (below?) and zip through as they launch themselves from the sea and desperately try to escape into the wet.
Though it is under the sea and beneath the island there is air. One walks on the ground even though their is no reason that would explain how they could balance upside down. It is a hidden place valued for many of the same reasons that make it so dangerous. The inhabitants are composed of hobs born from modern fairy tales, aliens. The fear and wonder has spawned tales of Grays, Lizard people, beings of pure light and other stranger breeds. These extraterrestrials live in crashed space vessels or futuristic cottages arranged awkwardly between the gray stone and aquatic foliage that waft in unseen currents.
Their are two ways to get to Underside. First find a path in the Knot and follow it around the island. But the paths are secret and treacherous. One wrong step and you drown. The second is to swim below until the reach the "sky" and make your way to the above/below floor. But save for a few kiths not many Changelings know the proper magics to survive the journey and so they either drown or miscalculate their entry and fall to their deaths paradoxically.
But there is no better place to study strange magics and wrest secret knowledge otherwise unheard of.