Perhaps the most common Daoist sacred space is the spectacular yet temporary structure unobtrusively called an altar (tan). Usually set up in large open fields or vacant lots, multilevel facades made of bamboo and covered with colorfully decorated paper simulate grand architectural spaces. These altars are the scene of the major festivals (jiao) that extend over several days. They enshrine such popular deities as the Jade Emperor and Zhang Dao Ling. Afterwards, the altars are taken down and the decorations burned. Several other ritual venues have been important as well, though not all intended for larger gatherings. Organizations within the various sectarian movements that have come and gone throughout the history of Daoism have typically practiced their own unique and often esoteric rituals. Always preceded by elaborate purification, these specialized rituals could take place either in natural settings, such as remote mountain retreats, or in enclosed meditative venues called “purity chambers.” There initiates would closet themselves for lengthy periods of disciplined mental focusing.