Horizon

Did you mean:


 * Horizon, the "headquarters" of Tradition mages?
 * A Horizon Realm, a pocket universe situated in the Umbra?
 * The "Horizon" is the Umbral term for the barrier separating the Near Umbra from the regions beyond:
 * The First Horizon, the Umbral barrier at the edge of Earth's atmosphere?
 * The True Horizon, also called Etherspace, which occupies the Umbral space between the edge of the atmosphere and the Asteroid Belt?
 * The Far Horizon, the dangerous outer edge, which maps to the Umbral space of the Asteroid Belt? This is usually what mages mean when they refer to "the Horizon."

You may also have meant:


 * Horizon: Stronghold of Hope, a Mage: The Ascension book detailing Horizon.
 * Beyond the Horizon, a Gamma World sourcebook.