Under the Mountain is the official name of Amarantha's infernal court and place of rule, from which she ruled all of Prythian.

After cleverly deceiving the seven High Lords and forcing them into submission, Amarantha named herself High Lady of Prythian and claimed Under the Mountain, a once sacred place for the Prythians, as her court, to which all must answer. It is said that Amarantha's place of residence, Under the Mountain, was fashioned and modeled after the famed Court of Nightmares, located in the treacherous northern Night Court, ruled by High Lord Rhysand and presided over by the Steward Keir, father of Mor.