Postcard Book with a box/case

Hello,
I have this travelogue postcard book from Munich. It opens like an accordion and there are several travel postcards from the city. At the end there is a box/case covered in black velvet.
Does anyone have any idea about the use of this box? Was is used to gather and save all the memorabilia from a trip? Or was it used to hide things in plain sight? Thoughts?

Thank you in advance for your answers!