People could be called into the Prison by Baha'u'llah when its door was closed to them.

“. . members of the Blessed Family came to visit and welcome us. I returned with them, and for the first time stood in the Presence of the Blessed Perfection. The state of ecstasy and rapture that possessed me was beyond description. The first words of Bahá’u’lláh were these: ‘We have brought you into the Prison at such a time when the door of meeting is closed to all the believers. This is for no other reason than to prove to everyone the Power and Might of God.’

https://bahai.works/Bahá’í_World/Volume_8/The_Passing_of_Munírih_Khánum,_the_Holy_Mother