The Hiroshi Labyrinth Stronghold
is a highly secured compound where the Realm Crystal
and the Sword of Sanctuary
are hidden. It was created by Cyrus Borg
and is located in Hiroshi's Labyrinth
Nadakhan found out the location of the Stronghold by tricking Misako. He then infiltrated it and defeated Borg's Droids to obtain the Realm Crystal.
Jay's last wish caused the events of Skybound to never happen, thereby keeping the Realm Crystal intact.
Sometime after the events of Skybound (and presumably after Season 9), the artifacts located in the Stronghold were transferred to a vault beneath Borg Tower.