The Arca of Recluse, sometimes referred to as the Cube of Recluse, is a powerful ancient relic found in the series.
The Legend of Heroes: Trails in the Sky the 3rdEdit
It was the Arca of Recluse that transports the group to Phantasma in Trails in the Sky the 3rd. Kevin Graham's guilt is the source of power for the Cube. It recreated a personal Hell in Phantasma just for him, as he was told by the Lord of Phantasma.