9 4 , ▁Pope ▁Clement ▁VII ▁in ▁ 1 5 2 7 ▁and ▁Marie ▁Anto in ette ▁in ▁ 1 7 8 9 . ▁Pass ages ▁and ▁t unn els ▁have ▁been ▁used ▁by ▁crim inals , ▁arm ies ▁( not ably ▁the ▁V iet ▁Cong ▁in ▁the ▁Vietnam ▁War ) ▁and ▁political ▁organizations ▁to ▁sm ug gle ▁goods ▁and ▁people ▁or ▁conce al ▁their ▁activities . ▁ ▁App earance ▁and ▁construction ▁Secret ▁pass ages ▁often ▁have ▁hidden ▁or ▁secret ▁back ▁doors ▁that ▁are ▁cam ou fl aged ▁so ▁that ▁they ▁appear ▁to ▁be ▁part ▁of ▁the ▁fire ▁wall , ▁or ▁so ▁that ▁they ▁appear ▁to ▁be ▁an ▁architect ural ▁feature ▁such ▁as ▁a ▁fire place , ▁a ▁built - in ▁sl iding ▁book case ▁or ▁another ▁feature . ▁Some ▁ent ran ces ▁are ▁more ▁elabor ately ▁conce aled ▁and ▁can ▁be ▁opened ▁only ▁by ▁eng aging ▁a ▁hidden ▁mechanism ▁or ▁lock ing ▁device . ▁Other ▁hidden ▁doors ▁are ▁much ▁simpler ; ▁a ▁trap door ▁hidden ▁under ▁a ▁rug ▁can ▁easily ▁conce al ▁a ▁secret ▁passage . ▁ ▁Some ▁buildings ▁have ▁secret ▁areas ▁built ▁into ▁the ▁original ▁plans , ▁such ▁as ▁secret ▁pass ages ▁in ▁medieval ▁cast les . ▁Some ▁medieval ▁cast les ' ▁secret ▁pass ages ▁were ▁designed ▁to ▁enable ▁the ▁inhabitants ▁to ▁escape ▁from ▁an ▁enemy ▁sie ge . ▁Other ▁cast les ' ▁secret ▁pass ages ▁led ▁down ▁to ▁an ▁under ground ▁water ▁source , ▁which ▁ ▁provided ▁access ▁to ▁water ▁during ▁a ▁prolong ed ▁sie ge . ▁ ▁Trad itional