A retreat can either be a time of solitude or a community experience. Some retreats are held in silence, and on others there may be a great deal of conversation, depending on the understanding and accepted practices of the host facility and/or the participant(s). Retreats are often conducted at rural or remote locations, either privately, or at a retreat centre such as a monastery. Some retreats for advanced practitioners may be undertaken in darkness, a form of retreat that is common as an advanced Dzogchen practice in the Nyingma school of Tibetan Buddhism.