The Clock Keeper's Boundary is one of the boundaries that is associated with one of the Seven Mysteries, in this boundary's case, it belongs to the First Mystery, the Three Clock Keepers.
Description
Exterior
The main part of the boundary is depicted as a massive labyrinth fille with gears, wheels, weights and other clockwork-based equipment. It so much of those things that it would be hard to navigate through it without getting hurt, as Yugi Tsukasa got hit by one of the gears while chasing after Yashiro Nene.
It is populated with several Clockwork Owl Guardians, supernaturals that are in the form of clockwork owls. The Boundary can also be reformed by Kako at will, transforming into a gigantic courtroom during the Trial of the Clock Keepers, as well as forming a long spiraling staircase that leads to the Boundary's Heart.
Heart
The Heart of the Clock Keeper's Boundary is a giant vault door that can only be opened with the Key that has the Clock Keeper's Yorishiro attached to it. The Door leads to a snowy and sleepy town that resembles a traditional snowy European Town.
The people who reside there resemble toys or dolls in European-themed clothing, and speak a language not familiar to Aoi Akane, and it is implied that both Kako and Mirai are of the same species as they are. If this is correct, then both Kako, Mirai and the inhabitants of the town are mysterious supernaturals whose bodies are comprised of clockwork and gears. It is to a point that should they be destroyed, Kako or anyone experienced in fixing machines can patch them up and "restore" them back to life in the process.
In one of the houses in the town lies Kako's Workshop. It is there where Kako fixed up Mirai and had a conversation with Akane regarding the "Root of the Problem".
