...There are various weak points in the Gauntlet where the worlds touch each other: Regio, where energy bleeds through from the Otherworlds but the Gauntlet remains strong; Crays, where the Gauntlet becomes so thin that piercing it becomes a simple task; and Shallowings, where the Gauntlet becomes virtually non-existant and, under the right circumstances, even the unawakened may cross without knowing it.... (c) Mage the Sorcerer's Crusade
http://whitewolf.wikia.com/wiki/Mage:_The_Sorcerers_Crusade