System of natural and artificial Caves and under mountain passages located on Planet Koken. The Forbidden Caves hold the Shafts of Knowledge and a Transdimensional gateway.
The shafts were made by the UNI, the transdimensional Gateway is much older and the original Forbidden Cave.
Reason for them to be "forbidden" is that the gateways can open passageways to other parallel Universes.

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