Shallow Realms are rare Realms on the very surface of the Umbra, right between the Gauntlet and the beginning of the Umbra, originally formed by magic for a specific task. As such, they require a creator, a connection to a Quintessence reservoir, a set list of people who are authorized to enter, and contact to the Material World. Den-Realms, which are used by the Bastet werecats, are a variation of a Shallow Realm.
Today, few, if any, Shallow Realms remain, the most prominent being the “Sleeping Lands” and the “Dreamtime” of the Australian outback, which date back to the High Mythic Age, before the division of science and magic. The others were created by a secret ritual before the Age of Reason and are such “grandfathered” into existence, many others simply withered away, when the shifting Consensus of Earth expelled them.