As to the Mashriqu’l-Adhkár, it is of the utmost importance. The purpose is this: A spot should be designated, even if it is a small place beneath layers of earth and stone, and it should, out of prudence, be kept hidden and concealed lest it arouse the hostility of the mischief-makers. At least once a week, it should become the gathering place of the chosen friends who have discovered the secrets and become the intimates of divine mysteries. It may assume any form, for even if it be an underground pit, that pit shall become a sheltering paradise, an exalted bower, and a garden of delight. It shall become a centre wherein the spirits are gladdened and the hearts attracted to the Abhá Kingdom.
— 'Abdu'l-Bahá, From a Tablet translated from the Persian