MONITORING PLACES OF DETENTION : A PRACTICAL GUIDE 20 National preventive mechanism This term specifically refers to mechanisms designated by a State Party as a “national preventive mechanism” under the OPCAT. Visit The term “visit” is understood in a broad sense to cover not only the actual visit to the place of detention, but also its preparation and follow-up. It covers the visit to an entire place of detention as well as more focused visits to specific detainees or concerning a particular problem, theme or incident.