Tested Travel loved visiting the Trois-Rivières Old Prison.
A working prison from 1822 to 1986, the prison ultimately closed its doors due to the unhealthy conditions.
There are guided tours of the cells and areas solitary confinement. Some of the guides are former inmates! It is amazing to see how inmates lived, how women and men were treated, and how hard prison life was.
Absolutely worth a stop!
However, as the guided tours are small, reservations are essential. Tours are available in English, but only on certain days. Be sure to check the website and make a reservation in advance.
Note that the prison is not open to children under 12. There are a few scary parts ( solitary confinement -- dark and scary) that might not be appropriate for the little ones.
More info here.